These do spawn in Nagrand. For a while there was a problem with them not respawning so you could only farm them after realm restarts but Blizz has fixed it.

(Please vote negatively on the old posts about them not spawning so they are hidden from all the new browsers now that it's fixed.)

Edit: here's the bulk of the info yall want:

Felmist <Mote of Shadow>
Swamp Gas <Mote of Life/Water>
Arcane Vortex <Mote of Mana>
Windy Cloud <Mote of Air>

Zapthrottle Mote Extractor <Engineering tool used to extract the motes.>