So for the rest of us who bought and enjoyed the first two volumes, with all due respect to all you who do not, it appears that the the final book in the trilogy will be released in Europe next week but on this side of the Atlantic we'll have to wait until late June of 2017.
Unless we order from overseas.
Amazon UK will set you back about $30 after shipping.
But I found a place that sells the paperback for $16 and hardcover for $19 with free shipping to USA:
If some of you guys don't like Graham's books, that's cool but the rest of us here enjoyed them very much and it's a pity there is no support for them and that we have to dig on our own to find out when/where to get them.
I pulled the trigger on the order from bookdepository.com - but if anyone else knows of a better deal, maybe they can post for others interested.