It is not possible to find any starter Pokémon in the wild, but you can obtain a few other starter Pokémon in ORAS. If when you beat the Elite Four for the first time, you can get a Johto starter from Professor Birch. When you complete the Delta Episode, you can get a Unova Starter from Birch, and when you defeat the Elite Four again, you can get a Sinnoh Starter from Birch. You also get given a Kanto starter by Professor Sycamore in Pokémon X/Y.
Edit: You can also find the middle stages of the Kanto starters in the Friend Safari.