Hemp twine is obtainable online. TWINE, not CORD. 1/8" diameter or a bit larger is recommended. It is strong, and not flexible like artificial sinew (waxed nylon). Linen is a good substitute. Even though hemp will not stretch as it is applied, it may relax with changes in moisture, so it must be sealed to stay tight. It was usually soaked with lacquer or some other sealant after being wound tight. Tung oil can work, but linseed oil will NOT. Linseed oil is designed to let water IN AND OUT. It is used on wood to prevent rot and decay from sun exposure in wooden roofs for example but after a good rain, it will let moisture leave the wood to prevent rot. It does not seal. Tung oil will seal with several applications. If lacquer is applied only to the surface, it will seal as long as it does not crack. If the material is soaked through, it will seal much better. You better make sure that your bindings are tight before you seal them, because once the sealant is applied, you will never be able to unwind the cord, and instead the entire binding will have to be sawed off and renewed with new cord should you ever need to remove the prod again or replace bindings that have loosened.