Greater Inscription of the Storm

Source
This item is a reputation reward; you must be with The Sons of Hodir to buy it from  for.

Unlocking the Sons of Hodir quests starts with They Took Our Men! in K3. This Level 79 (recommended), 42 long, quest chain requires the ability to fly and is unlocked at L77. Getting to exalted takes 27 days of daily quests (excluding turn ins of Everfrost Chip, Relic of Ulduar and other quests).