Even if one gets past the intellectual property issues with the manufacturers, the problem of sourcing parts is virtually insoluble. Integrated Circuit factories cost billions - and the old equipment is removed and junked shortly after the next generation of new equipment is installed. So, getting even a short run of some vintage chip (say for example, a Curtis chip) would require building the equipment to make the chip.
Once that is solved, there is also the issue that all of the older equipment used lead-based soldering, both internally and on the board interconnects. It is now illegal to manufacture these items in the European Union and many other places.
I serviced electronic musical equipment for over 30 years. Toward the end of that time, my largest single problem was locating replacement parts. (for that matter, not just electronic parts, but also items like replacement key-switches or buss bars for Hammond).
For that matter, I'd really like to get some GOOD 811A tubes for my ham radio amplifier. The Chinese tubes available today are pathetic. I bought over a dozen 1950's-1970's "NOS" tubes and managed to get three out of the lot that produce full power (600 watt out - the Chinese new tubes produced 200 watt out with the same input, and one blew a hole in the glass envelope after a couple of hours use).
Sorry to be the bearer of not so good tidings,
Jim
MoodyBluesKeys