There's billions of those in the junk yards. Look for any Volare, Aspen, Diplomat, LeBaron, Monaco, Gran Fury, or any truck up to the '93 models. I've rebuilt lots of them on the trucks when I was a suspension and alignment specialist at a Chrysler dealership in the '90s. Rust should not be an issue. What helped me was I had an 18" long forked air chisel bit for my air hammer that I broke, and I ground it down to fit those roll pins for rack and pinion steering couplers that were hard to reach. The roll pin you're after is the same size. The secret is the punch must be fat enough to not go inside the hollow pin, and it must not be tapered so it won't get wedged in the hole. Even when they're rusty, those pins don't come out that hard.

Be sure you can really see movement in that joint before you tear into it. I've had a bunch of these cars, (still have two Volares), and I had that steering wander on one of them. That one turned out to have a sloppy outer tie rod end. I have never come across a worn coupler on a car. I've only rebuilt them on the trucks, and I did a lot of them. The steering gear boxes need frequent adjustment too on the trucks and REAL often on the rear-wheel-drive vans, but never on the cars. Don't know why the cars don't develop that looseness. They use the same design.