Frostwolf Emissaries are level 55 Alterac Valley recruiters located at various spots throughout the largest Horde cities - Orgrimmar, Thunder Bluff, and the Undercity.
NOTE: They are only available during the monthly (Call to Arms: Alterac Valley).
See List of Orgrimmar NPCs, List of Thunder Bluff NPCs, and List of Undercity NPCs.