You might want to get in touch with Maggie in St. Louis. She runs the River City Riders board www.stlphins.com/rcr. That board was the St. Louis Scooter Club but they changed there name. Not a Burgman only club but there are a lot of Burgman riders in it. Maggie has a Burgman 650 in her stable of bikes.
I've only heard of one Burgman only group in the USA, a mostly defunct one down San Diego way. There's generally not enough Burgmans around any given city to support a dedicated group. I'm in Los Angeles and run a scooter group with lots of Burgmans in it. But I'd think twice about starting a Burgman only group.
Your best bet is to find a very accepting motorcycle group, one that's says "all makes & models accepted". Here's one in your area. http://www.meetup.com/stlmrg/ No promises, but it reads like a nice group of folks.
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