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.
I thought this was pretty poor, the first three books were interesting, I will not be carrying on with the series
good end of the series, from Luminea to fol. I thoroughly enjoyed it all rock trolls next