Unless you can find NOS parts, I doubt you'll find much currently made in the USA. Rock Auto is a good place to start the hunt, although you might have trouble finding parts for the 3100. I've bought some items from the various specialty (old truck) vendors. Mixed results on what you'll receive and some will overcharge you painfully on shipping costs. NAPA will have some parts. You can check them online. O'Reilly's may have some. I wouldn't waste time with Auto Zone...they seem to be focused on other things. Advance Auto Parts...don't know. Haven't tried these folks. If you have an old Chevy dealership where you live, ask them. There is a chance (slim) that they have old parts still in their inventory or warehoused off-site.
For the spring pins, changing bushings is naturally the best route, however check yours first. I've seen some which weren't overly worn and didn't need replacing.
I'm not a fan of sandblasting. Rust can be removed in other ways and unless you're just trying for a brand new look it won't hurt things.
