i heard somewhere that Japan has stricter emissions laws then north america
That's quite possible.. I know the emission laws are differant in some other countries and that's the reason why their Celica's are allowed to come stock with more power, I guess they must be missing something that North American cars have to reduce the amount of pollution. But Japan does have a really high octane in gas, so that helps a ton too, because I imagine since they only have higher grades of gas that their cars are tuned a bit differantly and they can utilize that higher octane.
As for GT4P well I imagine you can only get it in Japan right now, so get it that way (maybe you can download it online) and then have your PS2 chipped and there you go.