This item is a random drop in Feralas.
It has been reported to drop from the following mobs:
- Feral Scar Yeti
- Longtooth Runner
- Groddoc Ape
- Gordunni Brutes and Warlocks
- Hatecrest Warriors and Serpent Guards
- Ironfur Bears
- Sea Elementals
- Land Walkers and Cliff Giants.
The aggregated drop rate is given as about 0.5%. As this does not account for the fact that while you have this item - or after you complete the associated quest- it will not drop for you again, the drop rate should be considered somewhat higher.
The best method known to date is simply to kill creatures in the zone and wait for it to drop.