To make a good band, I would put a large-diameter sleeve of shrink tubing over the affected area, then shrink it with a heat gun.
Then I would remove the sleeve and trim out the part that fits where the band is supposed to be. Luckily the original is black, and gloss-black shrink tubing in large diameters is available. Perhaps a vendor could provide a manufacturer's sample of a short length of the product, then you could test it out and start producing and offering these replacements to the market.
Some Campag headsets have a similar issue with a rubber band covering an oil port.
I have some thick shrink tubing that it seems if I stretched it slightly might fit over a headset. I used a piece of it recently to modify the water spill-over level in a toilet tank!