If all the groups could start making it a priority to get to the Wilmington safehouse, that'd be awesome. Obviously, do it realistically. If you have a radio, you could have heard the broadcast. If you're in the city, stumble upon it. If you're on the outskirts, you can see a sign pointing you in the direction of 8th Street.

I just want to get everyone who is still active together, so we can begin to build as a group. 

-For those who never joined up with someone else, and are still way the hell out there, I'm not gonna bother writing a death scene (their characters can jump back in any time, and since they aren't with anyone else their death would be totally inconsequential). 
-If you are active, and the individual(s) with you aren't, just bring them along. They'll "join the group" and be an NPC for a while, either until they die or their owner reclaims them.