There's a type of rubber material, available in different thicknesses. It may be EDPM, but I'm not certain. Specifically what material people use to make their own has been mentioned on this site, but I don't know the exact thread. You can do a search on here.
Whatever it is, it's not reinforced, meaning, it doesn't have anything like nylon cord inside. It's a solid type rubber product.
There have been some reproductions for other models, and they are much less costly than old OEM stuff.
These aren't for your model, but just an idea:
http://shop.3wheelerworld.com/index....product_id=373
http://shop.3wheelerworld.com/index....product_id=374
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