Square belt. 1.2mm cross-section. 80mm dia / 251mm length. Wholesale might work. I need 3-4 just to get my own drives working (one in a chicklet-keyboard PET, at least 2-3 external C2N drives - two black PET-era, one (at least) white VIC-20/C-64 era). Wherever they come from US or UK, $10-$12 including shipping per belt is just not gonna happen. I don't need to use tapes on a daily basis, and if I didn't have some old Rabbit-format tapes, I probably wouldn't be doing anything with real tapes other than demonstrate to people how they worked (and why we were so happy to switch to floppies).
Ethan, these belts are very common in Brazil. They cost about R$ 2-4 (Us$ 0,50-1,00) each. If you and the group need some, I can buy and put it into an envelope.