You can find a lot of stuff like that if you keep an eye out for it, people selling a box of grandpas old books, or old women getting rid of their husbands junk thats been sitting in the attic for decades.
I've gotten a lot of very old editions of books that way, though so far nothing as good as those. Best I've got is my grandfathers "soldiers handbook" from basic training in 1942. Had my great uncles flight log from the CAP in the late '40s too, but that disappeared probably 15 years ago.