Head to Alterac Mountains. Goto the Ruins of Alterac (With all the Orges and Yeti guys) and find a brick wall with stairs leading up to a lonely goblin named Bro'kin. He sells Recipe: Frost Oil, for 25s (Limited Quantity), which usually sells for more on the AH. (I got 5g for each one).
EDIT: I can't just show the image on the site, gotta use a link