Try Jasper Auto Parts on the South Side. I have got parts thee for 25-30 year old vehicles, not sure about 50 year old ones though. Still worth a call. They are also good at trying to track something down for you.
Here is a link to a repro one for 70 U.S. There are a ton of places that list them for sale.
https://secure.cougarpartscatalog.com/d785.html
https://www.dearbornclassics.com/coo...n-shrouds.html