Sorry, I don't know about any online sources or retail outlets that would be available in the U.S.

What you could try is skim through the Helsport list of distributors: http://www.helsport.no/en/DISTRIBUTORS/
Helsport is a small, but reputable Norwegian outdoor brand. Hard to get hold of outside Europe, I would think.

If you REALLY want these pairs PM me and let's see if we can arrange something.

You could also try to make your own. It isn't exactly rocket science. The footsacks should have a loose fit, with two or three draw strings (elastic cord is a good idea).