Saw a wheel at a jy and it looks like a Mag 500 but it had/needed a trim ring. Looked like it was painted instead of chromed. I'll try to attach a pic but this place is NOT pic friendly!!
It depends on the car, they were put on everything from dodge, chevy to mustangs. I don't think they are particularly rare. I also don't know how much it would cost to get the wheels restored to the condition of new ones. You can get 15X7 magnums for around $100 a piece now adays and like $10 more for 15X8. I don't know just me though.
You can find them on ebaymotors for cheap sometimes. But if its junk yard treasures your after, then look through a few more till you find some that are in better shape.