Here are some on Ebay:
Genuine 1971 Chrysler 300 15 inch hubcaps wheel covers | eBay
It seems you need to search on a regular basis to find a complete set as they do come up from time to time. This set has what seems to be two pretty good ones for used condition but only two of them have the center decal - the other one is missing the metal decal.
Keep looking to build up a set eventually. That is what I had to do to build up a pretty good set for my car.
Show us a photo of your car if you would be willing.
Thanks