Great idea.
One good source for material of that sort is a farm supply store in any country area. They do everything from those odd bolt sizes and lengths that are unobtainium in urban areas through welding gear and materials such as rubber sheet. I bought a piece about one metre square for eight pounds. It about 2mm thick butyl and does not have any reinforcment,whichmay be better where parts are in relative motion as the nylon or whatever fibres could damage paint or other finishes.
I also saw a posting on the Ireland section from a guy who supplies fender extenders of similar material for less than 20 pounds.
