The Giant Grey Stonehoof (Giant Boar) is a normal mob at level 37 and roams around 34.8s, 6.6w in Giant Valley of Trollshaws. Be careful at the entrance, there Giants and Drakes (with 6400), if you hug the North wall in that area you should be able to attack the Giant Boar by itself.
Does anyone know if the flank can be looted by someone not doing the quest or is it a bound item?