Fallen - the archive on Venus mission has an area with three majors spawning. Kill them all and then wipe to have them respawn Vex - Venus patrol, fly to the citadel area and there are a 3-4 vex majors in the area. Hive - Earth patrol, just down to the left from where you spawn is a little staircase going down into the earth. Three hive majors spawn in that area.