Try making your own. I have used paper from a paper bag for an Allis Chalmers engine. At least for the Allis Chalmers, you have to carefully select a correct thickness gasket in order to maintain correct gap between the gears and the cover in order to keep it from binding (gasket too thin) on the one hand, or, not being able to develop good pressure on the other (gasket too thick). This specification is spelled out in the AC manual, not sure about the Willys manual!
Good luck!