I bought some of this food-grade neoprene tubing on eBay many months ago. It appears to be an exact match for the original.
https://www.ebay.com/itm/155048877120
I would highly recommend having a supply of this on hand, so that you can cut the tubing to fit without having to worry excessively that you’re cutting it too short.
I made three prior attempts to buy tubing on eBay, searching for “plastic” rather than “neoprene”. Nono of these attempts was very successful.
I also tried to obtain tubing from the folks who sold me the belt. They would only sell it to me precut, not in bulk form, and the price they were asking was comparable to the price of a new belt.
I should say in their defense that when I first purchased my belt on eBay, the package apparently did not contain the little Allen wrench which allows you to make adjustments. They were very helpful in sending me the tool and two replacement screws, which are always included with the wrench.