What about rubber belts for floppy drives? Spares will have perished as well...
Might not be a bad idea to make a wiki page somewhere and measure the belts / source generic replacements. This way vendor/part# of modern replacements can be had for old belt drive floppys and computer tape drives?
I think the audio cassette deck enthusiasts do something like this and the arcade CRT people are building lists of consumer TVs with usable CRTs.
-- Ethan O'Toole