I hate to say it, but I have really good luck with charity shops, and thrift stores in the states. There's at least one charity shop near us that almost always has really old books. I love antique books! I found one hardback book of sheet music, perhaps that wouldn't count as a book for some, but being a musician, it does to me......it's called what the children sing, and I can't find a date inside, but there's a handwritten inscription inside, to a child from an aunt, and it's dated christmas 1919. I paid three pounds for it. It's got all the nursery rhymes, some I've not heard before, and I thought it was a real find! There's another charity shop near us that often has brand-new, by that I mean just out, hard backs by some of my fave authors.