Concerned I could only get them in the UK
Found my first pair in an out door shop at about the half-way mark of the (92 mile) Cotswald Way. I had never heard of sock liners before. I was dealing with a blister and a "hot spot" and was blessed the rest of the way thanks to the liners.
Found similar products in the US when I returned; but none of the other brands came close in terms of all day performance; so I Googled them.
Mark me down as being greatly relieved because this year it is the 192 mile Coast to Coast trail and, because the CtoC is much further North - and runs east to west....I would be no where close to the shop where I first discovered them.