Since Ty introduced bringing a Pokemon to Swsh, there's a lot more you can do.
PokeBall Plus in LGPE/SwSh for a free Mew.
You can get infinite in RB using glitches, which can be transferred via Transporter, then Bank, then Home.
You can get one in HGSS and Japanese DP via DNS exploits. This requires old internet routers.
You can get one in Emerald via the Old Sea Map event. This probably isn't accessible to you, but if you AR'd one in you would be able to access the island and catch a "legitimate" Mew.
You can get one in My Pokemon Ranch by depositing 999 Pokemon from your DP copy. Hayley, (the NPC of Ranch) will ask to be delivered a single Pokemon Egg from your copy of DP. Once that is done she will give you a Mew, which can be transferred all the way up to SwSh.
You can also get one in Pokemon Go via A Mythical Discovery
I think that's all of them