Dust devil and whirlwind do not show up on vendors. I didn't pick dust devil when creating my character so I didn't have the skill for the whole game. There is only 1 skillbook of whirlwind found as a static item so if you want to respec once you start getting tenebrium weapons you are screwed.
I played the game and didn't see dust devil or whirlwind on any vendor and I checked every level and played for about 70 hours. The same issue occurs with walk in shadows. You either pick it at level 1 when making your character or you have to wait until you unlock the air elemental portal at your homestead which takes a while.
