Did ZOS forgot to release it? Seems weird when you consider that styles like Prior Thierric and Baron Zaudrus Arms Pack already released and their respective Dungeon DLC is like 1+ year newer than Harrowstorm DLC.
Well They finally released Castle Thorn... It will be in shop from 15.06.
Kjalnar's Nightmare will be later this year. Dont know when exactly tho. Its already in game, we just cant see it.