Here is a partial list.
- Lake Field Music Adult Music Camp
- Jamey Aebersold’s Summer Jazz Workshops
- Don Wright Faculty of Music Summer Programs
- KoSA Music Percussion camps
- Berklee summer programs for the deeply committed
- Jazz Works Canada in Ottawa
- Chethams Summer School for Pianists
There are many more.
BTW: I've been attending as a drummer for many years in both the USA and Italy. I'm planning another summer road trip to do just that again.