If I'm not mistaken, doesn't the National Pokedex unlocked after beating the game unlock the data entries for all these pokemon? I'd be entirely alright not encountering other-region pokemon until getting the National Pokedex or getting the National Pokedex from the start.
Edit:
Yeah, that makes sense. Still, though, if it ever gets made that these other pokemon don't show up until that point, that'd be cool.
Edit2: To clarify, while I like the idea of getting all pokemon from any region without the National Pokedex, I really only stumbled upon this thread because I was googling for a hack that allowed the catching of pokemon not normally in Platinum.
