In other restoration projects over the years, I have needed to find
leather belts.  My solution was relatively simple; talk to the
local harness maker/tack dealer.  They can usually find the correct
thickness of leather (or skin one down to the correct thickness), cut
it into a "strip" and make it into a belt of the correct dimensions.

It is possible to make a pretty strong joint by overlapping and
gluing.  I have made several belts this way that were strong enough
to drive a generator on an antique automobile; they certainly ought
to be able to handle lesser tasks.

Joe Teagarden

 [ I once saw old neckties spinning the generator!  -- Robbie