Kino said:
the men and women who made those plates are no doubt dead now
I wouldn't necessarily think so. Glass plates were still pretty common into the 1970s, and were still available *from Kodak* until 2002 (T-Max 100, 4x5 size only -- marketed for scientific imaging where flatness and dimensional stability were paramount). And the Slavich factory (in Ukraine?) is still making them in 9x12 size, though they're about eight bucks a plate by the time they get to Retro Photo in England, and shipping on top of that (shipping to the US is likely to be ugly, too).
I found a reference to Mimosa plates used in microphotography (aka microfilming), from a 1962 UNESCO publication; that's probably the one you found as well. I also saw a reference to a Mimosa print-out paper, likely from the same maker.
Yes, they might well be gone -- but there are still a fair number of folks around, even on the Internet, who were working adults in the late 1950s...