List of helmets with meta sockets

Set Pieces
The head pieces of Dungeon Set 3, Tier 4, Tier 5, Tier 6, PvP-70, Gladiator, Merciless Gladiator, Vengeful Gladiator all contain a meta socket. The headpieces of further high-end sets are also expected to have meta sockets.

Badge of Justice Rewards
These items can be bought from G'eras in the Terrace of Light at the center of Shattrath City for 50 Badge of Justices.

Terokkar Forest PvP Rewards
These helms can be purchased from:
 * Spirit Sage Gartok at Stonebreaker Hold
 * Spirit Sage Zran at Allerian Stronghold

in Terokkar Forest for the cost of 18 Spirit Shards.