So my Holy Paladin Dorathea finally got Hungerfen to drop the pants (Cassock of the Loyal) for this transmog.
I also finally got the Gloves Life Bearer’s Gauntlets to drop from the Fel Iron Box that you loot after killing the last boss in Heroic Hellfire Ramparts.
I’m still gonna try for the other pieces and besides, if they don’t drop that just means more cloth for my tailor to makes bags with to sell on the AH. =D