After hunting for one of these for a couple of days (in PoEarth) I finally got the second one I needed from "An Earthcrafted Assassin", i triple checked the name of the mob I was looting from before looting it. The first one was of course from a Vekerchiki Warrior.
I am guessing that any Vekerchiki who becomes fabled during the fabled event can probably drop it.
Edited, Jul 19th 2014 5:32pm by Zarmak