I attempted to farm Essence of Air http://www.wowhead.com/item=7082 last night in Silithus. However, I could not locate ANY of the creatures who should be dropping this item. Has anyone else noticed/attempted to farm these since Cataclysm came out?
Another option would be to farm up Essence of Water and have an Alchemist friend transmute them to Air for you. If I'm not mistaken the cool down on these low transmutes was removed.
I recently did Felwood and am pretty sure the elementals that dropped water are still there.