Try Mectrol (
http://www.mectrol.com/ ). They make standard belts up to 18 inches wide, with all sorts of wonderful surface treatments for your spec'd CoF.
We have used their stuff both times we built tread drive systems, and never had a problem with the belts (now the rest of the robot, that is another story...). These are industrial-quality mechanism drive belts, and not automotive timing belts. When they say they are "heavy duty" they mean it - we have abused them a lot, and the belts show almost no sign of wear. They are pricey, and don't understand "I absolutely, positively need it tomorrow morning", so you have to give them a few days to fill your order. But if you can handle the price and the lead time they are a good source.
-dave
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All thoughts contained herein are the result of having way too much fun in the sixties...