The centaur are located directly north of Freewind Post up against the cliffs that mark the edge of Thousand Needles, an area known as Splithoof Crag. It is a large camp and the different types of centaur are scattered through it, though the Galak Scouts seem to be more scarce than the others.
<name>, I entreat you to hunt these centaur down. They shall feel the wrath of our revenge. Attack the centaur camp to the north of Freewind Post! Let wrath guide your hand!