This is the 25 man version of the Death Knight Tier 8. There are two sets, one for tanking and one for DPS, although they look identical. The pieces were bought with tokens that dropped off various bosses in Ulduar (see below).
The tokens drop off various bosses in Ulduar. The tokens are for different sets depending on whether it is the token drop from 10M (for ilvl 219) or 25M (for ilvl 226). You can also purchase the 10M version of the helm and chest for 770 Justice Points each from by Arcanist Firael (Alliance) and Magister Sarien (Horde) in Dalaran.
The tokens drop from:
Helm: Mimiron (10 man) & Thorim (25 man)
Shoulders: Thorim (10 man) & Yogg-Saron (25 man)
Chest: Yogg-Saron (10 man) & Hodir (25 man)
Gloves: Freya (10 man) & Mimiron (25 man)
Legs: Hodir (10 man) & Freya (25 man)