Short answer: Look for yellow balloons.
Long answer: I read a post on Rex H.'s blog, What is your Deepest Fear?, called The Concert, in which he said:
I knew there would be booze and dope all around me but just figured I could handle it.... It took every darn second of praying my ass off to get through it. So the lesson learned is concerts sober are cool but bring a sober friend along for support!I left a comment and actually remembered to check with my Deadhead sponsee. In front of the sound mixer is the correct location, but reliably so only for the Grateful Dead and only at festivals. A better bet, for any jam band, according to my sponsee, is to look for a table with yellow balloons. This will be staffed with sober people. At Grateful Dead performances these folks are known as Wharf Rats. Their website even includes meeting lists (although personally I wouldn't call these AA meetings, or NA meetings or any kind of "A" meetings, due to their affiliation with something other than than these recovery organizations).
I hope someone finds this information useful.