There are a few companies that make replacement cassette deck belts, but they are sold by size usually not by make and model number.
http
/www. studiosoundelectronics.com/beltmeas.htm take spaces out of link before use...
you can also in some cases use rubber o rings in place of belts, there are many sizes available.
many large electronics supply stores have a selection of replacement belts.
although it is a lot of trouble to measure, order belts, it is possible to re-belt
an old cassette deck, if you really love cassettes