Double Fine are teaming up with the insane roadies at Mishka NYC to create a pair of Brütal Legend-themed T-shirts which are possibly the most awesome clothing-related things ever seen ever.
Look upon Mishka's works, ye mighty, and despair... for you can't buy them. They're for competition purposes only, with Kotaku (in the link) suggesting they'll be one of those offering them. The game's Twitter should also be another good place to look.
Don't bother entering though, Kroms will beat us all to them.