In Baldur's Gate, it can be gained in the Area North of Gnoll Stronghold from Jared, who offers this pair of boots as a reward when the polar bear on the other side of the river is killed. This requires a certain charisma and alignment to get this as a reward.
In Baldur's Gate II, this item can be gained from the Mithral Token Machine in the Asylum Dungeon.
|“||Boots of the north: 'The Frost's Embrace.' Stranded by his company for a sack of gold, Daviol the Frozen was left for dead in the midst of the Great Glacier. His dying curse echoed across the barren wastelands to the ear of Auril, Goddess of Winter. She smiled upon him, and his bare body was protected and preserved by his newly enchanted boots of the north. With them he crossed the ice land in pursuit of his would be murderers. Driven by rage, Daviol took his revenge upon his previous friends as they warmed themselves in a tavern of the closest city. After his thirst for blood was quenched, he continued to travel the frozen land, never to be seen again.||”|