The last I check for a small fortune you can get replacements from Airstream. You can order tambour material by the sheet or have it cut to size from various sources. Or you can do what I and others have done take apart and rebuld them with new backing material. It's labor intensive and smelly but not complicated. There should be a lot of stuff in the forums archives. Send me a PM if you want to discuss my technique.
Or, a lot of owners have decided it's not worth it to deal with the time and expense and replaced them with more standard doors. Also a lot on this you should be able to find in a search of the forums past posts.
Sail on silver girl. Sail on by. Your time has come to shine.