It's surprising what's out of print - try to buy a brand new collection of O. Henry's Complete works. (Famous American short story writer - look up "The Ransom of Red Chief"....)
To back up what George said:
I made a deal with a local used book store that they would inform me via email me of any photo-related books coming into their inventory (but then I've been a customer for 15+ years). I also make a point of stopping by even when I don't get emails. Through them I got a copy of Strand's "Time In New England", Ansel Adams' "The American Wilderness", plus I found out about obscure New England photographers like Chansonetta Stanley Emmons.