"Every farmer, every laborer, every fisherman can both read and write — and we think that books instead of being locked up in cupboards, far from the sight of students, should be distributed as widely as possible. The books of our library are therefore
passed from hand to hand without returning to the library shelves perhaps for years."
Try in the RABCK forum. That's usually where people give away books. It is considered polite to say what you are willing to offer in return, however. It can be offering to pay for the postage, or trade for some books you have that you don't want, or even something else, like a chocolate bar or set of post cards.