Great to see you interested! You might post on the main forum to get more responses.
But yeah, that seems to be the size of it regarding books for AM. I have to say I believe there's a market for another one as the last one was for v11 (tech reference). There have been alot of changes since then. If you get a book out there for AM, then there's very little competition at the moment.
Apparently AM sells to more people than any other 3D program. If you were to maybe sell at the trade shows that Hash attend/do a discount deal with sales of AM etc I'm sure you'd be onto a winner. People like to have a book in front of them.
PS I see you publish 3D World Magazine. Cool.