The guy that makes them has a store in Visby, Gotland, but Johan got it when that dude was selling his stuff on an open air market - I think at Foteviken. I've got stuff from there, but I can't remember the name of the place. The chain is quite different from the one you've got in the pic there. You actually have to be tied into Johan's, which is done when you buy it. His has no clasp on the back like the one in the pic, but the part wher you're tied in is the ring in the front. The ring is actually a knot.
Anyhow, this question has been asked before, so the name of the store might be in one of those threads, but for sure other examples like the one above will be posted there. -T