I just picked up 4 15X6 wheels in a local boneyard off of a `70 Caprice. I believe they were original to the car as the original paint on them was a perfect match to the car's body color (no rattle can job).
A few years ago I had a full set of steel 15X7's, but I sold them (more specifically, the tires that were on them) to a friend, and rather than returning the rims, he scrapped them.
I don't know what they came off of, but they're out there.
Eric