Yep, that is a tough one to find. I have an original on one of my '71 Challengers, and another one that is missing.
Seems like I seen where someone was repopping them, but can't remember where.
I couldn't find one of these so I had my metal guy make one. If you want one too, $45 plus shipping made out of galvanized and slightly thicker. The pictures where you only see one they are stacked on top of each other and you can see it's a pretty good match.