Pixiv Comic App for iOS
So, there are several illustration guide books on sale from Japan ( try CDjapan, Tokyo Otaku Mode, JBox, JList, Amazon Japan, etc etc). Did you know? You can preview some of the pages of each book for free, through the Pivix コミック ("komiku" in Hiragana alphabet) or Pivix Comic app for iOS. If you don't know Japanese, you will need to scroll through quite a lot of the available titles of Manga in there, sorry.....