convertible top question?

Hey all I just tore off my old top and going through and inspecting and fixing rust issues on the top frame. One question that do have is the substance that the staples nail into on the top frame it is like a rubbery leathery type substance is that stuff available somewhere? Can you buy that stuff somewhere? Mine is brittle on the corners where the staples go. any help on this would be great Thanks
Pat Faley
67 NB S Clone
69 convertible project
East Peoria, IL