Collect the Residue of Shadow 0/6 (Shadow Valley)
Kill shadow mobs, found throughout the zone and Loot a Residue
You will get a task update for these at any point in the quest. So, in the beginning when he wont talk to you, looting these will still get a task update, and after you have in the collars, you will already have that QTY. So, get this task when you get the other 2 and loot these (6) when you see them drop.