Second Center Camp and I believe they have a volunteer mechanism if you search around the main website. The opera, is that still happening? As Mr T notes, go through last year's theme camp lists looking for live music and the What Were When. Better yet, meet camps in your regional and help with sound at regional events and fundraising parties. Running sound for live musicians is much more interesting than for DJ's. If you have done field sound, there are always documentarians who could use better sound or sound post. Good luck.
increasing the signal to noise ratio with compassion