The Ravasaur Trainers were a faction of trolls found in Un'Goro Crater aligned with the Horde, rumored to sell the fabled Ravasaur mount (presumed to be the counterpart of a Wintersaber). However, there were only two NPCs that belonged to the faction, and neither would speak with a Horde player or offer them quests.
While the faction still no longer exists one of the trolls has returned to allow Horde players the opportunity to earn themselves a [Venomhide Ravasaur] though a series of quests and dailies.
Patch 3.2.0 (04-Aug-2009): The ravasaur trainer Mor'vek has returned to Un'Goro and will offer to help Horde players raise and train a Venomhide Ravasaur as a mount... if they can survive the creature's deadly poison.
This faction was removed sometime prior to patch 2.3.0.