If im not mistaken to find the boss via the rune stones you find it in the ruins in the mountain biomes ( where the big green strong orcs are or where skeletons are )
I hope that narrow it in a bit of where to look in the mountain biome.

Regarding finding the right location for the boss.. well that is tough i also used allot of time.
It turned out the boss was at a biome in the other end of the map and i would not have found the boss location without the help of the rune stones.
But that is also what is nice about the game, the map is randomly generated every time.

just a small sidestep / tip.. If you run around in the mountains then take some time to gather wolf skin and make that into wolf armour. Its allot better than troll armour.
I cannot remember maybe you also need the abiilty to make iron armour and iron items to be able to craft wolf armour.
Wolf armour also protect you against the cold so you dont need potions anymore to keep warm.
A good way to win against the wolf is a sword and a shield. when the wolf attack raise the shield and let it bite and then hit it and do the same over again and again.
( avoid fighting with a pack of wolf its though )
Yes you can also use bow and arrow but the wolf is fast and will often be near you and attack very fast
- Oh an pro tip.. befor going into ANY mountain area build a house at the edge of the biome so you can respawn near the biome so you dont have to run so far to get your gear again.