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.
Yes to Michelle's books. Absolutely not another one from Alan Steele.
Loved this book but, really loved the whole series. I will listen to it all again.