Chuck, it looks like the Cougars are not immune to the junk part syndrome either. I believe you had told me once before that your Cougar is a 69. Problem is that both the 69 and 70 Cougars are Cougar and model year specific for the senders. There are two utilized for the 69 Cougar. With out low fuel (C9WY-9275-A ID# C9WF-A) and with low fuel sensor (C9WY-9275-C ID# C9WF-C or D). Not much chance of finding the the low fuel version "C" as it was discontinued in mid 1979.
Don't know which vendors you have used in the past and since there are so many in the market now I'll let you be the judge of which ones not to contact. You remember all the BS Geoff (Stanglover) went through with the sender for his Mach 1.
NOS is still your best bet if not insanely priced. Green Sales (Which I have bought from) shows two of the C9WY-A in their inventory. These are normally NOS units bought from Ford Motor Company or from Ford and Lincoln/Mercury dealers. You can call or request a price online. Either way I would ask then to verify that it is a genuine Ford sender and not a re-pop someone has stuck them with.
https://www.rearcounter.com/C9WY-9275-A-parts57834.html
There is one I found on E-Bay but is proudly priced. Didn't look any further but there may be some others on the site reasonability priced.
The brass float that comes on most of the repo senders are thin walled junk and leak just as bad as the plastic versions do. Ford still sales the original brass float but can be found at some Ford/Mustang parts vendors cheaper. I believe the Tri-Five Chevrolet site (55-56-57) even suggests using the Ford float on the repop senders made for their cars. Ford # is COAZ-9202-A(***Replaced by "B"***). Just make sure the listing specifies genuine Ford.
Good luck with your search and let me know if you need any more info!