The stainless is pretty easy to polish. You can use a good polishing paste to clean it up. If it is very bad you can hit it very lightly with 0000 steel wool first, then move to increasingly fine polishing material.

I have never seen a 122 or an 1800 with any other kind of clip than the wire thingy. I have often thought that a more modern plastic type would be a good upgrade. The fenders tend to get a bit rusty around the holes those clips fit in and I think plastic would prevent it.

I don't know what part would work, but this place has just about any kind of fastener imaginable: http://www.restorationspecialties.com