Ok. So here is a little something to start off with. Yu Yu Hakush Gashu Art Book by Togashi Yoshihiro. I own a copy of this book and love it. Here is a scan of the book to the best of ability, so please enjoy!
I'm currently searching for the book of Yu Yu Hakusho Official Character's Book Reikai Shinshi-roku. If anyone has a link of a scan that'll be greatly appreciated. I have a character perfect file book, but I'm not sure if they are one and the same. :P Anyway enjoy the Gashu Artbook. I'll post the perfect file and more stuff soon! ;)