The Witcher 2: Assassins of Kings[]
Caerme is a steel sword in The Witcher 2: Assassins of Kings and can be crafted after obtaining its diagram as a reward for the quest An Encrypted Manuscript. Along with the Forgotten vran sword, Mourner (Dark Mode only), and Dancer, it is one of the best steel swords in the game.
The Witcher 3: Wild Hunt[]
Caerme is a steel sword in The Witcher 3: Wild Hunt, available as random loot inside caves in Velen and Skellige, and from guarded treasures.
One location where it can often be found (if not guaranteed) is the guarded treasure inside a crypt at Blandare's cemetery (north from the village), guarded by 3 wraiths.