Welcome to the Forums and the world of Vintage Argosys!
I suspect that your Argosy's air conditioner is an Armstrong, and as was posted by Argosy 7728, Inland RV is probably the best source for a new replacement shroud. When compared to other RVs the age of our first generation Argosys, there are many parts still available from the manufacturer . . . and there is a remarkable number of reproduction parts available from a number of vendors who are active here on this Forum.
- Vintage Friendly Airstream Dealers
Inland RV -- Corona, CAVintage Friendly Parts Vendors
Ace Fogdall RV -- Cedar Falls, IA
Out of Doors Mart -- Colfax, NC
Vintage Trailer Supply -- Vermont
Fantastic Vent -- Elkhart, IN
Zip Dee, Inc. -- Elk Grove Village, IL
There are many other, but the above are a sampling of sources of parts for our Vintage Airstream and Argosy travel trailers.
Something that you might want to consider before towing your Argosy a significant amount is the addition of a rock guard to protect those valuable clear Panoramic front windows . . . the deep wrap wing windows are now available only in Solar Gray tinted rather than the clear utilized on our Argosy travel trailers . . . and the cost of a new deep-wrap wing window it typically in excess of $750.
I am sure that your Argosy will provide you with much enjoyment as you learn more about its unique character!
Again, Welcome to the Forums and the world of Vintage Argosy ownership!