There was a single tier set for all hunter specs for tier 4.
This set is purchased with tokens that dropped off bosses in various raids.
Helm token – Prince Malchezaar in Karazhan
Gloves token – The Curator in Karazhan
Chest token – Magtheridon in Magtheridon’s Lair
Pants token – Gruul the Dragonkiller in Gruul’s Lair
Shoulder token – High King Maulgar