Actually uyou could get 2 of the third generation starters b/c ubecause you can get one in soul silverSoul Silver after beating redRed. also uAlso you can get the other second, third and fourth by starting a new game and migratemigrating them once uyou have 7 pokemonPokemon which takes about 20 minutes. You how ever
However, you would need to beat soul silverSoul Silver 3 times to get all the first gen starters unless uyou get a fire redFire Red /leaf green Leaf Green to migrate from. andAnd I believe uyou can get shieldonShieldon /blastidon Blastidon from the guy at the bottom of twisted mountainsTwisted Mountains in black versionBlack. although im
I'm sure by now uyou have xX/yY which is going to become the easiest way to get pokemon, theresPokemon. There is something like 450 available between them,them; the most out of any other version and it will let you get the first gen starters. alsoAlso thanks to the online pokemonPokemon bank and pc uPC you don't have to worry about the mass amounts of trades needed when uyou have to restart to get those other starters.