Whirlwind should be available from vendors, though I don't think there is an actual Dust Devil book. The other skills should all be available from vendors after a few refreshes if not the first time.
I have seen people say they've seen it on Aureus when they were level 4-7. But level 15+ I have checked countless times (I spent an hour quickloading to refresh his inventory) and he simply will not carry that skill book. Which makes me unable to respec, since Whirlwind is arguably one of the most powerful skills at my warrior's disposal (along with Flurry, for which there are skill books aplenty).
I understand Larian wants to hide some skills in the game, force you to explore the game to find certain skills. But there should be options to retrieve these skill books elsewhere once you've found (and used) them. I can't see a good reason for not putting the skill in vendor inventories after you've found the book. All it does is prevent me from respeccing the way I want. Or maybe change the respec process: Have a separate screen where you can allocate your stats and skills, and when you press 'finish' those become your new skills/stats and any skills you've learned that won't fit anymore are removed. Or allow us to pay obscene amounts of gold to receive skill books for skills we already know. Something, at least.
