All overpowered random drop weapons are removed in the PC version and only present in the unpatched Xbox 360 version. This weapon does not exist on PC Enhanced Version.

Within PC version, Devil is available from "Mysterious merchant" within act 2, on Ioverths path. Sold for 1876 orens

Devil is a steel sword found in The Witcher 2. There have been reports of a Diagram available from the asylum in Act 1 :

14x Iron Ore

2x Leather

2x Timber

2x Essence of Death

4x Essence of Water