In the Boston area we have a few cons, i see PAX East already on the list, here area few i'm aware of that would fit a meeting/outing of 405th members.
Boston comic (April 20-21st 2013) on which is 5 years old now and growing very fast
Anime Boston (May 24-26th 2013) which is very last anime con and pulls alot of people in from all over
Arisia (Jan 18-21st 2013) fairly large sci-fi/fantasy/gaming con