Craig Brougher wrote in 990903 MMDigest:

>  There used to be leather belting sold with a nylon or some kind of
>  plastic webbing inserted in it, like polypropylene ski rope, that
>  prevented it from stretching.  That way, you had the solidity and
>  grab of the leather, along with the stability of the internal webbing.

I have found a source for 1/4" round leather belting with something
like nylon sandwiched down the middle.  The industrial sewing machine
industry uses round leather belting just like we do.  I contacted a
source and they have confirmed they have the product.  (They even sent
an e-mail on Labor Day holiday!)  The source is:

  Westchester Sewing Machine Company
  tel: 914-627-5722 or 800-225-8342
  carusew@prodigy.net
  http://www.carusew.com/industrial/sewingmachines.html

Good luck,
Dave Allan