The Ripper-Horn Tribes are mentioned several times in the original tabletop books. Graktar, the leader during An Eye for An Eye is also mentioned in the sixth edition of the Beastmen army book, where he was the leader of the herd before Khazrak. When Graktar was wounded, Khazrak challenged him for leadership and managed to defeat him, ripping off one of his horns in the process. Graktar was then exiled.
Graktar also appears in one of Khazrak's quest battles.
While playing as Clan Eshin in the Vortex campaign, a hostile army belonging to the Ripper-Horn Tribe spawns close to your settlements in the Southlands, as part of an event during the Eshin campaign.
They first appeared in the Eye for An Eye mini-campaign for the first Total War: Warhammer game.