If the belts are so hard to find through Tamiya, why not try to find the right belt through an industrial hardware supplier?
Most of the information should be on the belt, and with some measurements you'll be able to find a belt that works - perhaps such a store may even be able to help you out if you bring along the belt. I'll admit it's not the easiest road, but it's worth doing that instead of being completely dependent on Tamiya to supply what is a standardized, non-RC component
