Honestly the selection is pretty poor in Atlanta, I pretty much get all my rubs and sauces via mail order. You can usually find Bone Suckin' Sauce at Whole Foods, but beyond that I can't help you.
Many of our own Brethren sell versions of their rubs and sauces, and they are better than anything you'd find at a store in Atlanta. Check out the "Brethren Sales and Ventures" section of this forum:
http://www.bbq-brethren.com/forum/forumdisplay.php?f=37
Another good mail order source is the Kansas City BBQ Store, they pretty much have everything:
http://www.thekansascitybbqstore.com/kc2/
Maybe some other Atlanta area Brethren can chip in with local sources, but I pretty much get all my stuff via mail. Expensive to ship but I haven't found a good local source.