Nah, there isn't an official (or unofficial) NISA group....
Or at least there wasn't, until now! NISAmerica Steam Group
. it's just me ATM, but feel free to join and advertise! It's unofficial of course, but I don't see NIS/NISA minding, especially since they haven't bothered with PC games so far as I know.
Please do join, fellow Steam users, it's rather empty here all by myself ~_~