Man, you're right. For NNP, it really does seem like there's not much out there. That was by far the toughest Google job I've had in a long time and I still don't have a specific NNP review for you. Check out the site below and see if anything there will help. I don't see a specific NNP exam review, but there are review books for different topics (infection, cardiac, etc.)
http://neoreviews.aappublications.org/
Good luck!