Getting replacement disk drive belts is a problem with many older keyboards. Someone on the Yamaha forum had a similar problem with their SY-77 and was unable to get an original replacement. The solution was to take the belt to a local VCR repair shop and get them to find one from a VCR that was as close a match as possible, probably a little smaller actually, as stretching is usually what causes these belts to stop working so you need something that fits a little tighter than than the one you are replacing.