So here is what I would recommend to start this sucker going. Think Globally - Act Locally. Start getting gigs going on your own. There is nothing stopping you from going to a GameStop or a Circuit City and have a HALO weekend that would raise money for a charity. The first thing is to go to the charity and tell them who you are and tell them what you want to do, as far a donating to them. Then create events. MAKE THEM HAPPEN. After years of doing it in the 501st, I can tell you that until the public knows your there they won't drop the events in your laps.
When you go to make events, make them something worth while to you and those that show (both trooping it and meeting the troops). I have done things like Trooper Olympics a couple of times. I set up courses where the public participates with guys in armor shooting Ewok targets with nerf guns, throwing frisbees through Death Star, bowling Jar Jar out of the way with items. we had an obsticle course that people did on a RAZOR scooter while in armor, dodging items and taking corners. Once we even got a SEGWAY for the obsticle course. Themes to an event and having public participation will throw things over the top. Even if you are the only one in armor to be there, the croud will love it. You can have a cadet corps that are local folks that could help out with pictures and donations. Create back drops that you can use for pics. Pre print pictures that you can sign your autogrpah to and give to kids. There are a million things to be done. Don't wait for someone else to do it for you. Go out and make it happen. Account for every penny donated and take it to the charity, thank the donators and thank the charity folks. You can even organize a childrens hospital invasion where you go and visit the kids for an hour or two and give them autogrpahed pics and take pictures with them.
Someone can make this happen. All you have to realize is that you are someone!