I managed to snag a copy of the fourth artbook! It’s gorgeous! It’s actually the Chinese edition; it’s smaller than the original release, paperback instead of hardback, and the paper’s lower quality, but I still love it!!! I also got it for a very decent price (around $35) so I didn’t get ripped off.
I now have four of the six manga artbooks, which is four more than I thought I’d ever get!