Blizzard has revealed that the Garrosh Heirlooms and Tusks of Mannoroth will be available for purchase during Remix: Mists of Pandaria!
These heirloom items were originally available as random drops from Garrosh Hellscream on Normal, Heroic, or Mythic (Originally Flex, Normal, and Heroic). At the end of MoP, you were guaranteed one weapon for your class on your first Normal or higher kill. These haven't been available since the launch of Warlords of Draenor.
Similar to Tusks of Mannoroth, you are able to purchase Garrosh Heirlooms using Bones of Mannoroth. These are drops from Garrosh Hellscream, the final boss of Siege of Orgrimmar on Normal, Heroic, or Mythic difficulty.
Each heirloom costs 2x Bones of Mannoroth and 8000x Bronze.
Bronze is the global currency from Remix, can be obtained from any activity or from scrapping items.