The only starters available anywhere in Kalos are the trios you get early in the game: you pick one of Chespin-Fennekin-Froakie at the beginning, and one of Bulbasaur-Charmander-Squirtle when you get to Lumiose City. After you beat the league, Shauna does offer to trade one of the Kalos starters that you didn't choose, and you can get all three starters from both of those trios by having the right people listed in your Friend Safari, but that's all.
If you want the other regional starters, you'll have to play ORAS. Being set in Hoenn, you obviously get to choose from Treecko-Torchic-Mudkip at the beginning, then Prof. Birch will let you choose from the other trios after completing certain milestones: Chikorita-Cyndaquil-Totodile (Johto) after you beat the league, Snivy-Tepig-Oshawott (Unova) after you catch Rayquaza and beat Deoxys to conclude the Delta Episode, and Turtwig-Chimchar-Piplup (Sinnoh) after you beat the league again with their postgame level increase.
