It took me 2.5 hours to do that whole step. Step 1: get a ghost that identifies the type of material you need Step 2: find these materials (I got the special material about 1 out of every 5-10 on average) Step 3: go to siege of the warmind (level 12) with a bad juju and kill the whole first room, using supers, grenades, and melees as much as possible. Then die and do it all again until it's finished. It is a grind but my friend got his today and he was destroying people with its special ability. Edit: I saw someone mention this below, but chests won't get you special materials, it must be the material in the game world to have a chance of the special material.