The first two sets I got from Ukazoo Books in Towson, Maryland, which is a great used bookstore to go to if you’re in the area. (Parking’s terrible, though.) The last group is from Goodwill. I wish there were more secondhand bookstores nearby! A lot of our local libraries have stopped doing book sales, too. Thrift stores are always good for book-hunting, though!
(I got home and realized I already have that exact copy of In Cold Blood. Oops!)