The Center for Sex and Culture puts it on here in San Francisco every May. They host all sorts of classes and events in The City and you can receive their emailer for free. Here's the link:
http://www.centerforsexandculture.org/
Hubby has always wanted to go but I've been dragging my feet. They do have a hands on hand-job class that sounds fun, but this being San Francisco the hassle of finding a parking spot tends to outweigh the fun of attending such a class.