[userbinator]

it's also extremely difficult (if not impossible) to make a 5.25-inch floppy drive independently, as it involves custom mechanical moving parts

The tolerances are not that high and the physical specifications are available from ECMA; most of the mechanical parts would not be difficult for a machinist, it's the heads which are the most difficult. The intersection of machinists and retrocomputing hobbyists is probably not that large, and 5.25" drives are still not really rare enough to attempt remanufacturing.