My wife and I recently purchased this entire set, excepting books 1 and 5, at our local library book sale. We are now looking for the missing volumes, so if anyone happens to have them laying around, and would like them to go to a good home, get in touch :)
Try a secondhand book site: I like abebooks.com, and there's also alibris.com. I'm slowly assembling a set of the Oxford Charles Dickens; every few months I pick a title I haven't got and search for a copy that's called "fine" or "very fine". ("Fair" copies are readable but may have markings, highlighting, etc., or be a battered ex-library copy.)
A used books search engine: http://used.addall.com. Bookfinder is owned by Abebooks which is owned by Amazon. Biblio is independent and often price competitive.
