The Witcher 2: Assassins of Kings[]
Looted from the body of the harpy queen in the harpy lair.
The Witcher 3: Wild Hunt[]
Harpy returns as a silver sword in the third game, this time in two versions:
Harpy (crafted)[]
Crafting Requirements 
Min. Required Level: Journeyman blacksmith
Harpy (relic)[]
This version can only be found as random loot inside caves in Velen and Skellige, and from guarded treasures.