There are two locations on cats that spawn the books the little room just east of where you drop in to the champ spawn area beneath bedlam. and the room directly to the south west of the altar. I was able to nab several of them over time. hard part is catching them spawn to know when. When I was hunting them on a regular basis, I was actually surprised how often I would happen into them and got both on a few occasions. Gave most away already though. Wish you luck the hardest part is getting that first one.
oh yeah one last thing....they will retain the color of the wood crafted with so make sure your using the right color you wan as they color the entire bookcase, i would recomment regular wood for best appearance.