Collect Amulets of Binding (always update) from several undead. All are found around Citadel of Gul'thex ( 692, 0, -720 ) /waypoint 691.87, -0.00, -719.66.
4 Gul'Thex high guards -- these spawn ONLY with the ring event mobs inside the citadel used for spawning Captain T'Sanne. There should be at least one in each wave, however, there are only two waves and then T'Sanne spawns alone. After that is a 30 minute respawn timer for the ring event to restart.