Methinks
Older units were run to death and or improperly maintained, so when they failed off to the rubbish heap they went.
OTHO those whom do own vintage units, may know what they've got and are hanging on.
Searching locally such as estate sales and Craigslist type offerings may yield better results when looking for vintage AC units. The things aren't exactly light, and the shipping would likely deter both sellers and potential buyers.
We have an older Friedrich "WallMaster",and dread the day it goes. Pumps out cold air and while not terribly efficient, gets the job done better than the electronic units sold today.
Only fly in the ointment is taking the unit out of the wall for cleaning at least every other year, and to oil the motor.
Many persons did not realise then or didn't appreciate the directions to clean and maintain older ACs, and this includes oiling the motor, along with removing built up dust,dirt and gunk.
So many people chuck an AC because it "won't cool" when the thing really needs a good steam cleaning and new filter.