If you're into antiques, you can check ebay and similar places for:
1. The Slayer's Guide to Gnolls, Mongoose Publishing 2001 [MGP0002] -- contains everything from Gnoll physiology to habitat, society, scenario hooks, and more. This is a d20 product released under OGL 1.0, so it's intended for D&D 3.X, but Pathfinder is a d20 game also.
2. Dark Folk - Trolls Orcs Goblins Kobolds Gnolls; RoleAids, 1983 (RoleAids707) -- Has a small amount of social data, from what Gnolls like to eat to what kinds of pets they prefer, and then it has a reasonably complete adventure that features gnolls (but the maps are weak) called "Wedding Sacrifice," for 6-10 characters of levels 3 to 6. Obviously, this is intended to be used with 1E AD&D, since that's all there was in 1983, but the ideas and fluff are still usable. I haven't read this product all the way through, so I can't vouch for it, but if memory serves, RoleAids stuff was largely crap. Giving them the benefit of the doubt, this may not be a wholly crappy book itself, but it is sure to bear some of the stench of other RoleAids foulness, so caveat emptor!