I have a 700 with the original rubber bumper (its crumbling) and it actually has yarn strands inside the rubber down the top and bottom edges, I guess so they could get the rubber to shape in the mold? It's so interesting how they made these and the tricks they used.
If someone had a tool & die made from an original mint condition bumper, I bet you could press out new bumpers made with, like, melted down car tires or something. There is a very small rubber making shop in my city but I have no idea if they take random joes off the street. It's not like they are getting any business, the building looks virtually abandoned but people are still working there.