There's always a "courtesy of..." under each image board and it seems like it's all books released for each film.

also, the inaugural special exhibition for the new Academy of Motion Pictures and Sciences museum in LA was on Miyazaki; they somehow gathered all these boards and notebooks in one place for several months. This was magical, and I give the curators props for doing this; they could have easily started off with a self-celebratory American/Hollywood franchise...

But I think they released a exhibition book to go along with this that has a lot of his artwork in there as well

You're welcome! I shared from AnimationObsessive's blog, and they did a great deal of research and showed the drawing image boards on paper from Mr. Hayao Miyazaki himself and the studio. This article I find unique, and some images have not been seen or public before. I recommend subscribing to their blog for more animation articles.