I've made that question a few weeks ago to the author himself, and this was his reply:
I don't know that I ever replied to this email of yours! I'm terribly sorry. I actually forwarded your email to my agent when I got it--and it was helpful in getting us to push Tor to put out more ebooks.
They aren't out quite yet, but book two is coming soon. We have to wait for Amazon to put it out for the Kindle first, since Tor promised them first crack at it. After that, it should show up in the other formats as well. We're hoping to have them all out by the end of the year.
Thank you so much for reading. I'm sorry to make you wait on the ebooks of the other two novels.