I'm not sure of any large/formal clinics, but the LBSs around here tend to put on clinics. Perhaps a shop near you would do something like this. Though it's already nearing the end of the season, here, so I wonder if clinics would have been in late Aug. or Sept.? That's kind of how they've been in this area.
Truly, though, most people just go out and try it without any formal instruction. You learn a lot just being on the course. We have a nice C race that is only 30 minutes long and a lot of brand new racers give it a try.