Well, hate to bring up "what used to be", but one of the most famous garagefests in the south was "Sleazefest", a now defunct live music event that was held annually in Chapel Hill. It was the brainchild of Southern Culture On the Skids, and a majority of the bands played the Local 506. Bands like the Fleshtones, Dirtbombs, Paybacks, Greenhornes, Detroit Cobras, Nashville Pussy, and many others played numerous times over the course of years that this was still going on. However, the Local 506 and the Cave which is nearby still book garage bands to play. There is also a killer music shop on the same street called CD Alley, which carries a shit ton of vinyl and cds from Arf! Arf!, Norton, etc. as well as more than enough titles from all your favorite garage, surf, and punk bands. Speaking of Sleazefest, I think it was inspired my a live music event called "Trashfest" that was held in Athens, GA, but I'm not even sure if that's even going on anymore...
Although it's not really garage, there's the "Heavy Rebel Weekender" event held in Winston-Salem, NC every July 4 weekend, and it's more centered around the psychobilly/rockabilly hot rod scene although they have booked some garagepunk bands over the years...