Found Ixthiar Doomcallers, Ixthiar Decimaters, Ixthiar Reapers, and other Ixthiar mobs at 18131, 12208 in Vale of Balor (in the Ixthiar Woods if you're using the Valmerwolf maps)
Doomcallers and Decimaters were orange to a level 39. Reapers were red and grape to a 39.