Top of the morning to you my friend and brother, I hope that other than the sock search you and your wonderful family had a great Christmas and are well.
I've got a pair of what you're looking for on right now sir, which I know came from Marks up here and I want to say are made in the US.
For the life of me I can't find them on the website now.....arghhh.
All the best to you all in the New Year, may it bring peace and fulfillment to you all.
I will add the maker down here if I figure out who they are.
This isn't them, but the 40 below and 50 below look a lot like what I have on.https://www.jbfields.ca/icelandic-products/
Well, since I'm staying home today - we're at a high of -15° and it's snowing on and off - I went online and bought a 2 pack of the 50 Below since I was in the market for some replacement heavy socks too.
I shall drop you a PM when they land or I'll text you what they're like.
All the best again.