The best place is Internet. I used to have a lot. Forbidden Gateway lasted only two books while Cretan Chronicles lasted only three. I'm currently writing one. I'm into traditional plots, as long as the author gives them a twist here an there.
Originality is the key.
I have all the gamebooks I want. I's have to say book 3 of the Cretan Chronicles, so I can finish that trilogy. A final FF story, written by the genre's masters, to tie all the books in together. In the region of 300. A more accurate count would require strict guidelines as to what exactly a gamebook is.