[kwhitefoot]

Attics and cellars of retired, or more likely deceased, engineers probably. Most such books were never in ordinary libraries and would be discarded when the new edition came out. The American Radio History [1] web site looks like a good place to start.

I have Babani's 1st and 2nd Book of Transistor Equivalents and Substitutes [1] and several National Semiconductor data books and application books from the 70s, '80s and '90s.

I almost never refer to them any more but they were so central to my life as an electronics engineer that I can't bear to throw them out.

[1] https://www.americanradiohistory.com/Bookshelf_Bernards_Baba...