Found: one ball of Regia Nation Color sock yarn in red and white. Sadly, there was only one ball, in a bargain bin, labelless.
Even if the hand-written label hadn't been there, I would have bought it. It's unmistakable.
I reckon I'll do black ribbing, heels and toes, and I'll still be able to reverse the stripes - but it won't be quite as amusing as the all-over striped version.
Next up -- seeking the red, white and blue, and the blue and white... Santa?