Officially licensed merchandise for twelve bands can be found at the new Rock Vault in Second Life. Avenged Sevenfold, Slipknot, Funeral for a Friend, HIM, Kings of Leon, The Ramones, Trivium, Iron Maiden, Bullet for my Valentine, Nickelback, Stone Sour, and Cradle of Filth are the bands represented, though not every one of them has inworld shirts to buy.
Whether there are inworld shirts or not (the price for all of them seems to be about L$150) each kiosk links to an online merchandise site where you can order the physical article. Don't go to to sleep quite yet, though. There's something much more interesting about this place than just selling tee-shirts -- thank heavens!