Does anyone have any books, or anything of the sort that has reference photos of backgrounds, especially in Japan?
Try flickr, that's where I used to go for japanese scenery porn. Speaking of scenery porn, this may be one of the few times r*ddit is actually useful.
Theres a wealth of this content on flickr. Start going through photographers favorites and you'll have a few thousand images saved in a day. Get a plugin called Save Images or whatever bulk image downloader and you can pull down galleries easily.
Those 2 will get you started.