It's at the San Jose GC store which is actually in Santa Clara. See their website at http://stores.guitarcenter.com/local/event/222/3931 for the official listing (but there is not much information there). Looks like they will have this every Saturday. It's only for 45 minutes, but the good thing is that they will let people try out the drums and other items that they have for sale; check with sales staff first.
I plan to go and check it out. I'll let you know how it is. Maybe they will agree to a longer time if all goes well.