The Great Forge has, to my mind, been likened to the Dwarven version of Vahalla. It is the place the Dwarves go to once they die - the home of the Great Dwarf.
As such, it is possible it has no actual location. Think of it in this way - can you plot "Heaven" on a map of the universe?
The Lore for Ice Tooth Cave states that nearby Anvil Rock is thought to be the anvil on which the Great Dwarf forged the Dwarves from the earth, thus it is a sacred place to them, hence their meetings on that very spot.