Yasuomi Umetsu sketchbook

Does it exist ? As someone that likes to draw, a sketchbook is a reality for me, so I can only assume that a master artist like Mr Umetsu, has one too. In fact, he probably has more than one :)
I recently bought Mr Umetsu's Key Animation Drawing books and even though I prefer the content of Artbooks i.e. original artwork, I liked what these books offer. They basically show much of the creative process (mainly storyboards), that led the artist to draw what we see in the show itself. This is something I expect in a sketchbook. Not only original artwork (drawings that we haven't seen, even on the existing artbooks), but also rough sketches of the characters, in different positions. The "Yellow Star" artbook and Mr Umetsu's "Artworks" book, contain some of these sketches, which I proudly own.
The sketchbook would definitely be a collector's dream item, probably only reachable, by those that know Mr Umetsu himself at this point. But there's always that tiny little detail, called money, that will surely amount to astronomical figures, if and when this sketchbook is avaiable for grabs ^_^