Nether Vortex

[Deathkillshot]

So the questions are:
Is the only way to get it is from the last T5 quest (for Kael'thas)? Is it 100% chance from that quest?
Is there a chance to get it from other quests in the chain?

[Brutone]

IDK. I only noticed that every second warrior of Onyxia already transformed his deep thunder to stormherald while on Blackrock I wasn‘t able to find anyone with that weapon.