Does Mixx publish any of the artbooks?
The artbooks (illustration collections) do not currently have any english publishing. And, I have not heard any rumors about Mixx picking it up. Currently, there are the original Japanese and Chinese versions available in soft or hardcover; French has a hardcover version of 1; German has hardcover versions of 1-5. These are the only versions I am aware of at this time. The Materials Collection (artbook 6) is a relatively new release and is only available in softcover Japanese.