The most common place I found and bought 450 wheels over the years when owners knew little about them, was from the trunk of 15 inch 71-2 B-bodies. They carried a G-60-15 Goodyear Polyglas.
The last single 450 wheel I found was 2 years ago.
I visited a guy's farm who I knew had quite a few Mopars in his day but had been away from them for years.
Asked him if he had any plain 15x7 rims laying around.
He pointed to the field and said he thought there was one there if I could get it off this vehicle he hadn't been using for years.
I had my doubts but as I got closer to it I couldn't believe what I was seeing, a 450 rim!
Seized on the hub, I spent 1/2 an hour with a sledge hammer to the tire but I wasn't going home without it.
It was on an old 8 1/4 rearend that was powering a manure spreader and that is no BS!!