I had a 1987 Deville with a system like you describe. It was FWD and probably had a totally different bolt pattern so I didn't bother looking for it, but now I know I can look for retainers from a 1983 LeSabre.
My Rally wheels are rusted and nasty. Also, as part of being cheapjewcao, I buy used tires already mounted on steelies that fit my car so I don't have to get them mounted (and I can swap in my yard easily so I can put on worn tires during the summer, all-season tires in fall/spring, and studded winter tires in the winter).
So, since I usually have not just steelies but rusted, unmatched steelies, I've acquired wheelcovers. These meet my aerodynamic wishes
and OEMness standard, as they were standard equipment on the 1980 LeSabre. Eventually I would like to get racing discs but these are functionally pretty close, they fit nice and tight to the wheel's rim, they look decent, and I got the first three pretty cheap (as well I'm now getting a bunch for free).
I bought four pizza pans to make pizza pan racing discs but never did finish that project.
Racing disc:
Pizza pan:
1980 LeSabre OEM:
---------- Post added at 10:04 AM ---------- Previous post was at 10:03 AM ----------
I think
all of the above would look better with whitewalls. I know the OEM ones sure do.