Hotz Mats are nice, I had a bad experience ordering with them though. They claimed to have sent me order but it never came. I eventually got my money back, but never saw any hard proof that the order was made or shipped. It was during a facility move so that could have been the cause.
I do have a mat from these guys though:
http://corseceng.com/fabric-mats/It's an older one printed at Spoon Flower, I'm not sure who they're using now but you can't get a 6x4 anymore (that and international shipping is ridiculous). If you've got a high DPI space image you could always print it through Spoon Flower yourself though.
Other options are Monday Knight Games, or getting someone to airbrush some felt for you.