Well I found a new source of cheap belts for my Unimat 3 today. A
swimming pool equipment supplier and contractor. They have a variety
of "O" rings that fir various bits of pool equipment and some of them
are the same size as the lathe belts. Try to go befor your belt dies.
It is much easier to match one up that is continuous than a broken
one.

From the specs I have:
long belt is: 3.25" x 0.20
Short belt is: 2.75" x 0.20
Auto feed belt is: 1.75" x 0.15

Keep on turning!

John