I think @Tom Lane knows of some, but they're DB.
The two that I'm fully aware of aren't exclusively DB, but they are exclusively jazz:
Louisville Jazz Workshop
The Louisville Jazz Workshop is held in Louisville, Kentucky, at the University of Louisville sometime in late June or July. It's a jazz combo camp, meaning you'll play in a group of 6 to 9 other players about at your skill level and be lead by an experienced jazz instructor. You'll play through tunes, get coaching on your instrument, there are master classes, lectures, jam sessions for beginners, intermediates, and advanced students, and evening concerts. There's no audition to sign up but there is one for placement. The audition is very casual and is just used to figure out your skill level. It's limited to 18 and above, mostly folks over 50.
The other is
https://centrum.org/program/jazz/ which I've never attended myself but I have friends who have, and given that it's closer to me that Louisville, has been on my radar for a long while. There is an audition for admittance but I believe that they tell you exactly what they're looking for and so you can shore up your skills as necessary. Still, it doesn't sound like a camp for beginners; mostly highschool and college age folks looking to have some exposure to jazz royalty: John Clayton, Jeff Hamilton, etc.
Ah, two more:
Lynn Seaton's Jazz Double Bass Workshop
Lynn Seaton Jazz Double Bass Workshop at UNT | Division of Jazz Studies is exclusively for DB and exclusively for jazz. Mostly high school kids trying to get into UNT's jazz program. About a dozen campers. I went one year and had a blast. Lynn's a great teacher and player. Lectures and group performances all day, concerts in the evening. Well worth it for anyone serious about jazz DB.
And UNT has their own jazz combo camp:
UNT Jazz Combo Workshop | Division of Jazz Studies I've never been but I imagine it's a bit more like Port Townsend the the LJW, in that it's mostly high school kids trying to get into UNT's jazz program. And, I'd say Denton, outside of Dallas is less "vacation-condusive" than Port Townsend or Louisville. Louisville has some fine restaurants and some sights to see.
Ah, one more:
Sligo International Summer School and Jazz Festival In Sligo, Ireland, John Goldsby is usually there teaching. I haven't been there yet, but I almost went last year. Ireland's a bucket list destination, Galway is breathtaking, and this is a jazz workshop where every evening, all of the concerts and jam sessions are held in the local pubs. Sounds like a blast!
But there are others on the East Coast, Canada, and in Europe. The best thing to do is to setup a Google Alert to receive links every day about what's going on.
HTHs!
