This WoW set features the full Valorous of Faith transmog, which is the priest tier 7.5 (25-man) raid set. Valorous of Faith is obtained by looting Wrath of the Lich King bosses and purchasing some set pieces straight from the vendor with gold. Dropped tokens can be traded for set pieces via Dalaran tier vendors.
How to Get Priest Tier 7.5? By purchasing from vendors and slaying Naxxramas/Obsidian Sanctum bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Priest Tier 7.5 Transmog: [25-Man Drop Locations]
Note: Priest have two different sets with the same exact look. Tier 7.5 priest armor tokens can be used to purchase any of the set pieces.
Head: Crown of the Lost Conqueror [Kel’Thuzad] in Naxxramas
Chest: Breastplate of the Lost Conqueror [Gluth] in Naxxramas
Hands: Gauntlets of the Lost Conqueror [Sartharion] in The Obsidian Sanctum
Legs: Legplates of the Lost Conqueror [Purchase from Vendor] in Dalaran.
Shoulder/Leg Vendor (Alliance): Arcanist Ivrenne [37,55] in Dalaran.
Shoulder/Leg Vendor (Horde): Magistrix Lambriesse [65,23] in Dalaran.
Redeem Token Vendor (Both): Paldesse [43,49] in Dalaran.
Set Name: Valorous Garb of Faith (hover for set bonuses)
Shoulder: Valorous Mantle of Faith
Chest: Valorous Raiments of Faith
Hands: Valorous Handwraps of Faith
Legs: Valorous Pants of Faith