Hit a couple other airgun related forums, too. Check out the American Vintage Airguns forum, the Yellow Forum, and the Crosman Airgins Forum, as well as the Canadian Airguns forum.
Your best bet is to hit someone that has a junker in the box that isn't missing the same parts.
The little "shoe" that pushes against the piston is a PITA part to make, and is usually kacked. Fragile by design.
Cheers
Trev