I've noticed this too in other zones, and I think it has to do with population density of a particular area. I'm not 100% sure on how it works, but I think the more people there are in a zone, the more pets there will be. Respawn times on more commonly found pets might also depend on how many players are in a zone. Don't quote me on any of this, though, as I'm just guessing.
It could also be that the zone was just underpopulated with pets. Check the official bug/pet battles section of the WoW forums, and if others have reported this issue, hopefully Blizzard will increase the number of spawns.
Good luck and keep trying, you'll find something eventually!