Where do i get flying mount?

From wow.incgamers.com

Beta is capped at lvl 67 and flying mounts are lvl 70 only. So at present moment the answer is - nowhere.

Update : Temporary flying mount vendors and trainers are manually spawned in Honor Hold or Thrallmar.

Regular flying mount vendors and trainers are (will be) available in Shadowmoon Valley.

See also Places where you can fly and Flying mounts