Hi Bob,
Is there any of the original printed text on the belt? This can be a real help in finding a replacement which are almost always standard parts easily obtained from an online bearing shop (amazon). I recently was able to obtain new belts for my old Myford ML7 lathe and milling machine just from these numbers. Some are metric and some are imperial but the key dimension is usually the inside length of the belt.
If you can find anything then go to amazon or similar and type the details in and search.
Edit: It looks like a standard vee-belt so the chances are good. Dooh! K 21 is a 21" K style vee belt (8mm wide).
HTH
Jon