This claims to be the World's largest selection of new & used audiobooks on cassette and compact disc - CD. Full length - unabridged, abridged & dramatic books on tape, etc..
AmazonUK audio books
BooksonTape- Publisher of unabridged audio books.
Hope these are of interest, got them from google, just put your title in and loads came.
Haven't used them myself, so cannot attest to quality.