Ugh. If you like a book full of silly arguing and an ending that barely resolves anything go ahead. As usual Rosalyn Landor great in narration.
There are many reasons why a book might be unavailable.
Sometimes a book goes temporarily out of print - and sometimes no audio version has ever been recorded. Audible wants to give you the most complete selection we can and we'll keep adding series and filling in gaps as quickly as possible.