Just talked to Jerven.
They currently have no distributors outside of Scandinavia. There seems to be some issues of proper labeling of the products, as well as a way of receiving payment from abroad, before they can market themselves outside Scandinavia.

(Business idea: become a US distributor?)

However, I was told that anyone who is interested can email them at post@jerven.no and they'll work something out. English is fine!

I'll add some info on sizes:
On the sizing page you can see the different sizes and weights in centimeters and grams.
On sizes:
The Original shape is NOT long enough to stretch out inside.
On insulation:
Original (also Hunter and King Size shapes) have just the aluminum-covered inside.
Thermo (also Hunter and King size) has 80grams/square meter insulation
Extreme has 200 g/m2 insulaton.

Any questions I can answer -- including digging up a supplier if the factory can't deliver -- feel free to ask.