WoWDB

I've found that the Forest Creepers in Hillsbrad Foothills are a pretty good choice for farming for this. They're fairly close together, respawn decently quick and are found in numerous amounts all across the zone.

The Black Widow Hatchlings in Duskwood are pretty good as well, but there are some battlepets also located in this area of the forest and people will be killing these spiders to battle, so amounts may vary.

Good luck! This item is a pain to farm because of the relative low droprate of it. :)