There are actually quite a few clubs in the Thumb and SE MI... have you seen any of these sites?

http://www.lmb.org/clubs.htm

http://www.bicycle-gifts.com/busami.htm (tri-city cyclists looks like it's in your area)

http://bicycling.about.com/library/clubs/blclubmi.htm

i don't know how far you're willing to travel to ride with a club... there are also a ton of organized rides in MI throughout the summer. check out http://www.mikebentley.com/bike/ for a great list of midwest bike rides. a google search for "michigan bike rides" turns up quite a few hits as well.

also, if you're a mtn biker, check out www.mmba.org. they have a TON of resources for Michigan Mtn bikers.

good luck, and happy riding!