For me the quest for replacement outer vent cover springs has ended. A local Ace Hardware store stocked an extension style spring that is the right wire size and the right coil size. Cost was $2.00 each. With the help of a MAPP gas torch the ends were straightened until the right number of turns remained and the legs were at the requisite 90 degree angle. After reheating, the spring was then quenched in cold water to re-establish the temper and set the memory. Then the legs were cut to length. This is the result compared with the remnant of an old one.
Installed they look like this.
The only difference is that on the original one would be a left hand winding and the other a right hand so that the leg against the door would be on the outside on both sides. Functionally there is really no difference and I'm happy. I still think someone should offer these for sale.