Attempting to acquire this will probably see you on your way to completing the collectibles for South Vern, the drop rate is terrible. I've got a third of the collectibles done (including 2 of legendaries) just trying to drop this one piece of the recipe.

EDIT: Took many days (could only take soo much each day, 5 days since original comment), but i finally dropped part 6 from the smaller area just over a bridge with a guard stood on it (saw this spot mentioned in discussions around the web). Once i started on that spot(see image below), it dropped after about 30-40 mins. I have practically all the collectibles done at this point, but at last i can move on.