A couple suggestions:
Look for a LBS near you that is listed as a Shimano Service Center - There should be one in the Milwaukee, Racine, Kenosha area, maybe even in the northern Chicago suburbs. They may have an assortment of NOS replacement parts. I remember Racine had an old-time bike shop, but can't recall the name.
Or - See if there is a local bike Co-Op and rummage through their bins of miscellaneous parts.