I'm an intermediate bass player living in the UK. I'd like to attend a short (one week or a long weekend) bass course around New York or Boston. I'm 32 and don't really want to attend a course that's almost all kids (the Berklee one seems to largely for under 18s).
I think the bass collective in NY offers one-week, two-week, three-week programs.
Another option could be Jeff Berlin's Player School in Florida. I heard a lot of good things about it and they also offer "short" programs.