Le Quartier général de la Scoia'tael is one of the few merchants in Vieille Wyzima from whom Geralt can buy items, if of course he is on good terms with the Elfes at this point in the game. Le nain explains that while he would rather be fighting at the front, Yaevinn has designated him quartermaster. After all, you can not wage war without gold!
If Geralt has chosen the Scoia'tael path, then the quartermaster can be found on the western outskirts of Vieille Wyzima, not far from the Portail de la digue. Si Geralt s'allie avec l'Ordre, ce marchand est le Quartier général de l'Ordre.