I have a car manufactured in 1972, that I stilll use regularly. I can buy ALL the parts for it off the shelf. As long as there is demand, someone somewhere will keep the demand supplied. My car is an MG Midget. Same with cameras. At the moment the used supply is such that it is uneconomic for anyone to specialise in supplying new/refurbished, but in time it will happen. For example, if you took a common and good model - say Olympus OM - there are only so many bitsthat wear out. You could totally specialise in these buying up all old bodies, remanufacturing the few bits you need, and selling out as new re-built. They would cost 100s but in time I am sure it will happen.