The Making Game of Thrones production blog has a great interview with Will Simpson, storyboard artist for the series. Simspon’s worked in comics over the years (I just realized he drew some Hellblazer arcs written by Garth Ennis!) and has largely shifted into storyboard and animation work. Some of his storyboard work is featured in Inside HBO’s Game of Thrones, the production companion book that HBO has recently released.
The interview also refers to a book containing Simpson’s storyboards… and that, too, has recently been revealed as part of a special collector’s edition (Pre-order: Amazon US, Amazon UK), paired with Inside HBO’s Game of Thrones, two maps, and a presentation box. The portfolio sounded as if it wasn’t all that many pages… but reading the details more closely, it suggests the book is just as large as Inside…, which would be quite a lot of storyboards indeed!