I bought several belts for a dollar each at an estate sale several years ago that were probably pretty old. Every one of them broke almost immediately after putting them on the sander. I don't know if it was just age or if they got hot sitting out in their garage in the summer heat around here but I learned my lesson about buying old belts. So I basically bought some long sheets of course sandpaper that I am still using up.
I also did some research at the time about repairing them. I was not able to find anyone that sells the adhesive tape that is used to join them. What I found was that they are either proprietary or were only available to commercial producers in huge bulk rolls. There were a couple of videos about a DIY repair using some sort of glue but even the youtuber said is was not a very reliable fix.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.