Jeez i would have responded in my own thread sooner had i known someone was gonna revive it after so long
Torin: I would either check out stores in Tokyo like Echigoya that have flyers and info on Airsoft fields in the area. You will every once and awhile meet some english speaking players who will be more than happy to bring you along and show you how things are done.
You're best bet is to find a field, give them a call and just go. The fields I was able to go to were all extremely friendly and the players were almost all extremely polite.