I am surprised that no one mentioned suppliers of leather belting for
industrial sewing machines.  Before I started rebuilding player pianos,
I had an industrial sewing machine business for 40 years.  I used to
buy leather belting from my sewing machine supplier; he had two sizes
-- small and large -- and also had two qualities.

I only purchased what they call "hair on" leather because this was the
hardest.  It had been the top of the cow hide, and would not stretch
so much as the other grades.  He also sold the hardened hooks and the
splicing tool.  You could also purchase the V-belt in rolls with the
groove for making V-belt to size using the same splicing hook.

I still purchase supplies from him and if anyone is interested I will
find out if "hair on" leather is still available.

Hector Sanchez