Any good research Uni's psych department will have some TMS studies going on over the course of a year. You'll probably have to do a repetitive task and they probably won't be doing any diagnostics (for that you're way better off with a FMRI or EEG study, where they're often happy to share the data with you), but if you're just curious about the experience you can probably get paid a pittance to try it out.

Interesting! I will ask my friend in the neurology department if she knows anything :)