For minor damages, a standard paint job. For seriously messed up situations, add fiberglass cloth and epoxy, the boat/yacht people use them all the time. Just saying, I know the question was about buying one but if that ends up complicated, there are ways to fix or even fabricate those. Anyway, the easiest place to try is perhaps your local bumper repair shop. Sometimes psychology points us in the wrong direction. If you damaged your car bumper similarly, you'd want it fixed and painted. But if it's a smaller piece on a motorcycle, you want to buy a new one.