There are ad hoc meets that happen fairly regularly. Some organized here or E90 post http://www.e90post.com/forums/forumdisplay.php?f=49
, others on other Bimmer boards, and some through BMWCCA. Plus more general car stuff. Because of weather, it's kind of sporadic until you get into May or June.
People talk about Schomp for Denver dealership. Others can probably advise. I'm in Boulder.