Where can I find an antique book?

For my wedding, I'm making a modification of the secret compartment book idea, but with a red silk pillow inside with our rings on it for the ring bearer to carry. I know it's sacrilege, but since I'm going to be cutting the book up I'm looking mainly for aesthetics. Where can I find inexpensive, hard-bound, pretty-looking preferably antique books? Thanks for any help!