I think the detroit region scca club is probably a good bet. I think there is a private sports car club that runs events in the area as well, the name escapes me at the moment.
I say show up and run in a novice class, I always give mad props to people running autox with temp plates :D
Every club you find is going to have its own subgroups, the serious guys to the fun guys. You just have to feel them out.
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
"Hella Functional - Raced, Not Hard Parked"