Tusks of Mannoroth

The Tusks of Mannoroth were the tusks of the Pit Lord Mannoroth. After Grom Hellscream slew Mannoroth and freed the orcish horde from demonic enslavement once and for all, Warchief Thrall placed the skull on a large memorial in Orgrimmar with a plaque commemorating Grom's sacrifice.

Years later, Grom's son Garrosh Hellscream would take the skull and cut it into two items: the larger part would decorate Garrosh's throne in Grommash Hold, while the tips would serve as his shoulder plates. Baine Bloodhoof noted in Jaina Proudmoore: Tides of War that he believed this was a disgrace to Grom's memory, that the tusks were no longer a symbol of orcish freedom, but a symbol of Garrosh's personal power.

The tusks drop from Garrosh after the final battle of the Siege of Orgrimmar. They are -quality DPS plate shoulders.

Source
This item drops from Garrosh Hellscream in Siege of Orgrimmar.