Stamp Thunderhorn is a level 35 food vendor located in the Darkmoon Faire camp, which is only available during the monthly Darkmoon Faire event. It rotates each month to a different location. One month it will be south of Goldshire in the human starting zone of Elwynn Forest. Then, it is off to Kalimdor where it is southwest of Thunder Bluff in the tauren starting zone of Mulgore. Then it travels to Outland near Shattrath City.
See List of Elwynn Forest NPCs and List of Mulgore NPCs.