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.
Of all the books I have listen to by LLM, this one is my least favorite. Parts are just to unreal and too many things were not addressed.
but, please, please, please, never use this narrator again. She can't do men's voices. Her voice is pleasant, but not for this!