Mojotone has a pretty large selection. Click on each color/style to see more options.... http://www.mojotone.com/amp-parts/tolex-tweed-colors
You also might look at fabric shops and automotive interior supply shops. Who says that you have to use tolex?
Good luck! Let us know how it goes. I've considered re-covering one of my amps and am interested to see how it turns out....
Look for tolex. The vinyl does not take to the adhesives like tolex does. It's more expensive but it works better with the adhesives. Anything less will stretch too much and will separate from the backing, and or bubble up and generally be a pain in the ass to work with. Plus tolex takes a hit better than vinyl from the fabric store. I make guitar cases and have been through a number of materials. Tolex. Upholstery fabric is not the same. Tolex was originally made for car tops and is much tougher than upholstery material.
What about the cloth/material XITS amps uses? Does anyone know if that available anywhere?