I'm gonna start answering little by little I don't actually expect anyone else to do this. This is kind of a personal project that is being shared with anyone who wants it. If you're looking for a specific Pokemon, I recommend using Ctrl+F or Find in Page to find the Pokemon you're looking for
I will mention two methods for version exclusives most of the time. Remember Masuda Method is (almost) always an option.
Bulbasaur: Catch Combos, LGPE, Viridian Forest
Ivysaur: Friend Safari-Grass, XY
Venusaur: Evolve Ivysaur
Charmander: Catch Combos, LGPE, Route 3
Charmeleon: Friend Safari-Fire, XY
Charizard: Catch Combos, LGPE, Any outdoor location or Evolve
Squirtle: Catch Combos, LGPE, Seafoam Islands
Wartortle: Friend Safari-Water, XY
Blastoise: Evolve Wartortle
Caterpie: Catch Combos, LGPE, Viridian Forest
Metapod: Catch Combos, LGPE, Viridian Forest
Butterfree: Catch Combos, LGP, Viridian Forest, or Evolve
Weedle: Catch Combos, LGPE, Viridian Forest
Kakuna: Catch Combos, LGPE, Viridian Forest
Beedrill: Catch Combos, LGE, Viridian Forest or Evolve
Pidgey: Catch Combos, LGPE, Route 1
Pidgeotto: Catch Combos, LGPE, Route 16
Pidgeot: Catch Combos, LGPE, Any outdoor location, or Evolve
Rattata: Catch Combos, LGPE, Route 1
Alola Rattata: SOS chains, USUM, Route 2
Alolan Raticate/Raticate: Evolve
Spearow: Catch Combos, LGPE, Route 22
Fearow: Evolve or Catch Combos in the air on Route 22
Ekans: Catch Combos, LGE, Route 3
Arbok: Evolve or Horde Encounters on Route 19
Pikachu: Catch Combos, LGPE, Viridian Forest
Raichu/Alolan Raichu: Evolve
Sandshrew: Catch Combos, LGP, Route 3
Alolan Sandshrew: SOS chains, UM, Tapu Village
Alolan/Sandslash: Evolve
NidoranF: Catch Combos, LGPE, Route 22
Nidorina: Evolve or PokeRadar, DPPtBDSP, Route 221
Nidoqueen: Evolve
NidoranM: Catch Combos, LGPE, Route 22
Nidorino: Evolve or PokeRadar in XY Route 11
Nidoking: Evolve
Clefairy: Catch Combos, LGPE, Mt. Moon
Clefable: Catch Combos, LGPE, Mt. Moon or Evolve
Vulpix: Catch Combos, LGPE, Route 5
Alolan Vulpix: SOS chains, US, Tapu Village
Ninetales: Catch Combos, LGPE, Route 7 or Evolve
Alolan Ninetales: Evolve
Jigglypuff: Catch Combos, LGPE, Route 7
Wigglytuff: Sandwich hunting, SV, North Province Area One or Evolve
Zubat: Catch Combos, LGPE, Mt. Moon
Golbat: Catch Combos, LGPE, Rock Tunnel
Oddish: Catch Combos, LGPE, Route 1
Gloom: Catch Combos, Route 12, or Evolve
Vileplume: Catch Combos, LGPE, Route 21 or Evolve
Paras: Catch Combos, LGPE, Mt. Moon
Parasect: SOS chains, USUM, Route 11 or Evolve
Venonat: Catch Combos, LGPE, Route 24
Venomoth: Catch Combos, LGPE, Route 14 or Evolve
Diglett: Catch Combos, LGPE, Diglett's Tunnel
Alolan Diglett: SOS chains, USUM, Verdant Cavern
Dugtrio: Catch Combos, LGPE, Diglett's Tunnel or Evolve
Alolan Dugtrio: SOS chains, USUM, Haina Desert or Evolve
Meowth: Catch Combos, LGE, Route 24
Alolan Meowth: SOS chains, USUM, Trainer's School
Galarian Meowth: Masuda Method, SwSh
Persian: DexNav, ORAS, Mirage Spot North of Route 124 or Evolve
Alolan Persian: SOS chains, USUM, Malie Garden or Evolve
Psyduck: Catch Combos, LGPE, Route 24 or Mass Outbreaks, Obsidian Fieldlands, LA
Golduck: Catch Combos, LGPE, Cerulean Cave
Mankey: Catch Combos, LGP, Route 3, or SOS chains, USUM, Route 3
Primeape: PokeRadar, DPPtBDSP, Route 225, or Evolve
Growlithe: Catch Combos, LGP, Route 5 or SOS chains, USUM, Route 2
Hisuian Growlithe: Mass Outbreaks, Cobalt Coastlands, LA
Arcanine: Most likely Catch Combos, LGPE, Route 7 or Evolve
Hisuian Arcanine: Evolve
Poliwag: Chain Fishing, XY, Route 14
Poliwhirl: Chain Fishing, XY, Route 16
Poliwrath: Catch Combos, LGPE, Cerulean Cave or Evolve
Abra: Catch Combos, LGPE, Route 5
Kadabra: Mass Outbreaks, Obsidian Fieldlands, LA
Alakazam: Evolve (B2W2 trade SRs in Accumula Town could be fun tho)
Machop: Catch Combos, LGPE, Rock Tunnel
Machoke: Catch Combos, LGPE, Victory Road
Machamp: Evolve
Bellsprout: Catch Combos, LGE, Route 1 or Horde Encounters, XY, Route 14
Weepinbell: Catch Combos, LGE, Route 12 or PokeRadar, DPPtBDSP, Route 224
Victreebel: Catch Combos, LGE, Route 21 or Evolve
Tentacool: Chain Fishing, Route 128, ORAS or Catch Combos, LGPE, Route 19
Tentacruel: Catch Combos, LGPE, Route 24 or Evolve
Geodude: Horde Encounters, XY, Victory Road
Graveler: Catch Combos, LGPE, Rock Tunnel
Golem: Evolve
Ponyta: Catch Combos, LGPE, Route 17
Galarian Ponyta: Masuda Method, SwSh
Rapidash: Catch Combos, LGPE, Route 17 or Evolve
Galarian Rapidash: Evolve
Slowpoke: Catch Combos, LGPE, Seafoam Islands
Galarian Slowpoke: Masuda Method, SwSh
Slowbro: Catch Combos, LGPE, Seafoam Islands or Evolve
Galarian Slowbro: Evolve
Magnemite: Horde Encounter, ORAS, Route 110
Magneton: Catch Combos, LGPE, Power Plant
Farfetch'd: Catch Combos, LGPE, Route 12
Doduo: Catch Combos, LGPE, Route 17
Dodrio: Catch Combos, LGPE, Route 17 or 18
Seel: Catch Combos, LGPE Seafoam Islands
Dewgong: DexNav, ORAS, Shoal Cave
Grimer: Catch Combos, LGP, Power Plant or PokeRadar, DPPtBDSP, Route 212 South
Alolan Grimer: SOS chains, USUM, Hau'oli City
Muk: Catch Combos, LGP, Power Plant or Evolve
Alolan Muk: Evolve
Shellder: Chain Fishing, Y, Route 8, or Catch Combos, LGPE, Seafoam Islands
Cloyster: Catch Combos, LGPE, Seafoam Islands or Evolve
Gastly: Catch combos, LGPE, Pokemon Tower
Haunter: Mass Outbreaks, LA, Coronet Highlands, or SOS chains, USUM, Thrifty Megamart
Gengar: Evolve
Onix: Catch Combos, LGPE, Rock Tunnel
Drowzee: Catch Combos, LGPE, Route 11
Hypno: DexNav, ORAS, Route 121 or Evolve
Krabby: Catch Combos, LGPE, Route 10
Kingler: Catch Combos, LGPE, Route 12, 13 or Evolve
Voltorb: Catch Combos, LGPE, Power Plant
Electrode: SRs in pretty much any game or Evolve
Exeggcute: Catch Combos, LGPE, Route 23
Exeggutor: Catch Combos, LGPE, Route 23 or Evolve
Alolan Exeggutor: SOS chains, USUM, Exeggutor Island
Cubone: Catch Combos, LGPE, Rock Tunnel
Alolan/Marowak: Evolve
Hitmonlee: Catch Combos, LGPE, Victory Road, or Evolve
Hitmonchan: Catch Combos, LGPE, Victory Road, or Evolve
Lickitung: Catch Combos, LGPE, Cerulean Cave
Koffing: Catch Combos, LGE, Power Plant, or DexNav, ORAS, Fiery Path
Weezing: Catch Combos, LGE, Power Plant or PokeRadar, DPPtBDSP, Route 227, or Evolve
Rhyhorn: Catch Combos, LGPE, Cerulean Cave
Rhydon: Friend Safari, XY, Rock or Evolve
Chansey: Catch Combos, LGPE, literally anywhere you'll get it eventually
Tangela: Catch Combos, LGPE, Route 21
Kangaskhan: Catch Combos, LGPE, Rock Tunnel OR Masuda Method
Horsea: Chain Fishing, ORAS, Sealed Chamber
Seadra: Catch Combos, LGPE, Route 11 or Evolve
Goldeen: Chain Fishing, XY, Route 3
Seaking: Chain Fishing, ORAS, Safari Zone or Evolve
Staryu: Catch Combos, LGPE, Route 18
Starmie: Catch Combos, LGPE, Route 18 or Evolve
Mr. Mime: Catch Combos, LGPE, Route 11
Galarian Mr. Mime: Masuda Method
Scyther: Mass Outbreaks, LA, Obsidian Fieldlands or SOS chains, USUM, Poni Plains
Jynx: Catch Combos, LGPE, Seafoam Islands
Electabuzz: Catch Combos, LGPE, Power Plant
Magmar: Catch Combos, LGPE, Pokemon Mansion
Pinsir: Catch Combos, LGE, Route 14 or SOS chains, USUM, Lush Jungle
Tauros: Catch Combos, LGPE, Route 14 or PokeRadar, DPPtBDSP, Route 210 South
Paldean Tauros forms: Sandwich Hunting, SV, or Masuda Method
Magikarp: Chain Fishing, XY, Route 3 or literally anywhere
Gyarados: Lake of Rage or Chain Fishing, XY, Route 3
Lapras: Catch Combos, LGPE, Route 19
Ditto: Catch Combos, LGPE, Pokemon Mansion 2F
Eevee: Catch Combos, LGPE, Route 17
Vaporeon: Sandwich hunting, SV, pretty much anywhere, or Evolve
Jolteon: Sandwich hunting, SV, West Province Area 3 or Evolve
Flareon: Sandwich hunting, SV, Glaseado Mountain or Evolve
Porygon: Catch Combos, LGPE, Route 7
Omanyte: Masuda Method
Omastar: Evolve
Kabuto: Masuda Method
Kabutops: Evolve
Aerodactyl: Masuda Method or SRs, USUM, Seafolk Village
Snorlax: Masuda Method, Catch Combos, LGPE, Cerulean Cave, or Evolve
Articuno: Dynamax Adventures, SwSh or SRs, USUM, Ultra Wormholes
Galarian Articuno: Event only
Zapdos: Dynamax Adventures, SwSh or SRs, USUM, Ultra Wormholes
Galarian Zapdos: Event only
Moltres: Dynamax Adventures, SwSh or SRs, USUM, Ultra Wormholes
Galarian Moltres: Event only
Dratini: Gift from Benga in W2, or Catch Combos, LGPE, Route 10
Dragonair: Friend Safari, XY, Dragon or Evolve
Dragonite: Catch Combos, LGPE, anywhere in the sky or Evolve
Mewtwo: Dynamax Adventures, SwSh or SRs, USUM, Ultra Wormholes
Mew: Faraway Island Resets, Emerald
Chikorita: Starter resets, HGSS or Masuda Method
Bayleef: Evolve
Meganium: Evolve
Cyndaquil: Starter resets, HGSS, or Masuda Method
Quilava: Evolve or Time-Space Distortion hunting
Typhlosion: Evolve
Hisuian Typhlosion: Evolve or Time-Space Distortion hunting
Totodile: Masuda Method
Croconaw: Evolve
Feraligatr: Evolve
Sentret: PokeRadar, Route 202, DPPtBDSP, or MM
Furret: Evolve
Hoothoot: SOS chains, USUM, Lush Jungle
Noctowl: PokeRadar, DPPtBDSP, Route 210 or Evolve
Ledyba: SOS chains, USUM, Route 1
Ledian: SOS chains, USUM, Route 10
Spinarak: SOS chains, USUM, Route 1
Ariados: SOS chains, USUM, Route 10
Crobat: SOS hunts, USUM, Lush Jungle or Evolve
Chinchou: Chain Fishing, XY, Shalour City
Lanturn: DexNav, ORAS, Route 107
Pichu: SOS chains, USUM, Route 1 or Odd Egg, Crystal
Cleffa: SOS chains, USUM, Mount Hokulani or Odd Egg, Crystal
Igglybuff: SOS chains, USUM, Route 4 or Odd Egg, Crystal
Togepi: PokeRadar, DPPtBDSP, Route 230 or Mass Outbreaks, Cobalt Coastlands
Togetic: Massive Mass Outbreaks, LA, Cobalt Coastlands, or Evolve
Natu: SOS chains, USUM, Akala Outskirts, or PokeRadar, DPPtBDSP, Route 224 (Swarm)
Xatu: DexNav, ORAS, Safari Zone or Evolve
Mareep: PokeRadar, DPPtBDSP, Valley Windworks
Flaaffy: PokeRadar, DPPtBDSP, Route 222, or Evolve
Ampharos: Sandwich hunting, SV, North Province Area 1 or Evolve
Bellossom: Evolve
Marill: Sandwich hunting, SV, East Province Area 2
Azumarill: Sandwich hunting, SV, West Province Area 2
Sudowoodo: Sandwich hunting, SV, Casseroya Lake
Politoed: Chain Fishing, XY, Route 19 or Evolve
Hoppip: Horde Encounters, XY, Route 7
Skiploom: Flying Sandwich hunting, SV, South Province Area 5 or Evolve
Jumpluff: Grass Sandwich hunting, South Province Area 3 or Evolce
Aipom: Mass Outbreaks, LA, Alabaster Icelands
Sunkern: Grass Sandwich hunting, SV, South Province Area 1
Sunflora: Grass Sandwich hunting, SV, South Province Area 1 or Evolve
Yanma: Horde Encounters, XY, Route 10
Wooper: PokeRadar, DPPtBDSP, Route 212
Paldean Wooper: Poison Sandwich hunting, SV, South Province Area 1
Quagsire: Ultra Wormholes, USUM, Blue Wormhole or Evolve
Espeon: Psychic Sandwich hunting, SV, South Province Area 3 or Evolve
Umbreon: Dark Sandwich hunting, Violet, Glaseado Mountain or Evolve
Murkrow: Horde Encounters, XY, Route 15
Slowking/Galarian: Evolve
Misdreavus: Ghost Sandwich Hunting, SV, Casseroya Lake
Unown: DexNav, ORAS, Mirage Cave South of Route 107
Wobbuffet: Friend Safari, XY, Psychic or Evolve
Girafarig: Psychic Sandwich Hunting, SV, West Province Area 2
Pineco: Bug Sandwich Hunting, SV, South Province Area 2
Forretress: Steel Sandwich Hunting, SV, Casseroya Lake or Evolve
Dunsparce: SOS chains, USUM, Route 2
Gligar: Horde Encounter, XY, Route 19
Steelix: Massive Mass Outbreaks, LA, Cobalt Coastlands or Evolve
Snubbull: Friend Safari, XY, Fairy, or PokeRadar, DPPtBDSP, Route 209 (Swarm)
Granbull: SOS chains, USUM, Poni Wilds
Qwilfish: Chain Fishing, XY, Route 8
Hisuian Qwilfish: Mass Outbreaks, LA, Cobalt Coastlands
Scizor: Evolve
Shuckle: Friend Safari, XY, Rock
Heracross: Fighting Sandwich Hunting, SV, Socarrat Trail
Sneasel: Mass Outbreaks, LA, Obsidian Fieldlands
Hisuian Sneasel: Mass Outbreaks, LA, Coronet Highlands
Teddiursa: Friend Safari, XY, Normal
Ursaring: Massive Mass Outbreaks, LA, Crimson Mirelands or Evolve
Slugma: Friend Safari, XY, Fire
Magcargo: Ultra Wormholes, USUM, Yellow or Evolve
Swinub: Mass Outbreaks, LA, Alabaster Icelands
Piloswine: Friend Safari, XY, Ice or Evolve
Corsola: Chain Fishing, XY, Route 12
Galarian Corsola: Masuda Method