Ahhhh yes the latest fad in gold farming.
Obviously Throne of elements is the best place but its camped to hell.
Scald(bladesedge) is pretty good for primal fires
Netherstorm is good for primal manas. Expecialy the place just outside of area 52 with the manawrathes and wyrms. Or the kirin var village ruins with the mana ghosts.
Shadowmoon valley has a few spots for elemental air but its pretty spread out.
Nagrand Halaani basin is good and fast killin for Primal water + the mobs are not immune to frost.
There is a lake at the North edge of Terrokar forrest that spawns fishes that drop Primals. This used to be a good secret spot but its pretty camped nowadays too.
Primal earth and life should come from the Gathering profession
But if your server supports it you can farm the Bog lords north of swamprat post in zangarmarsh for Primal life.
And the various Earth elementals in Nagrand for Primal Earth.
Primal Shadow is also good from the voidspawns in Nagrand or Hellfire.
Over all Primals are a solid way to make gold and its easy and mindless. Try focusing on the primals with good AH value on your server.
Ive released this guide as an article with slightly more info here
