Timeworn Heirloom Armor Casing

The Timeworn Heirloom Armor Casing is sold by the following vendors:
 * Krom Stoutarm (Ironforge) or Estelle Gendry (Undercity):

During some holidays or events, the following currencies may also be used to purchase this item:
 * Timewalking: Auzin, Cupri, Kiatke, Mistweaver Xia:
 * Lunar Festival: :
 * Midsummer Fire Festival: / :
 * Hallow's End: / :

It is also a quest reward from Completionism.