Has anyone checked out the Dolmenwood setting that Gavin Norman and Greg Gorgonmilk have been publishing in Wormskin? I think it could be pretty easily adapted to Hyperborea if one wanted.
It's a fey-influenced wood with human inhabitants who are changed by the nature of the power there. I'm always leery of faerie and fey stuff for Hyperborea, but the ice elves that are described as the faeries in this history seem like they would fit right in with the myth-derived nonhumans of Hyperborea. Also would make a good fit with Joseph Salvador's "Beyond the Ice Fall" from AFS 6
I was reading the history of the area in Wormskin 4 this morning. It seems like the rise of this faerie power could slot nicely into the time after the Green Death, when the downfall of the Hyperborean sorcerer-tyrants has left power vacuums all over Hyperborea. The coming of the submen in later centuries would fit nicely.
The map in Wormskin 1 makes it seem like the area is about 60 X 100 miles is needed, so like 2.5 X 4 hexes on the Hyperborea map. I can easily see putting it in the Gal hills, either in the north (Hyperborean east!) or near Dunwich; north of Brigands Bay; or east (Hyperborean south!) of Larchmere Yys, depending on how you want to adapt the surrounding culture: Keltic, Viking, etc. It would also make for some pretty fascinating consequences to put it near Orcust on the Skarag Coast, along the Savage Boreal Coast, or even in New Pictland. Near the Striped Gulf and the headwaters of the River Leng is also a possibility.
Anyhoo, worth checking out.