I'd be all for a simple Pandora logo. Maybe someone could whip up a concept image and a few of us could send it to one of those custom t-shirt maker companies.
The quality of CafePress' clothing/merchandise, and their prints, is really quite good. So, yes, they certainly do exist. I can't comment on Zazzle, though, which is their main competitor (they offer quite different merchandise, outside of their clothing range).