Our friend who is cooking for us has just borrowed a bottle of soy sauce. She says she could not find it in the supermarket. Curiously, I had the same experience a couple of weeks ago in Asda. I looked everywhere, under sauces, exotic food, anywhere with small brown bottles, and could not find it.
It seems odd as Asda on-line confirms they sell a whole range of soy sauces, including their own brand. That's how we normally get it. However the deliveries come from local supermarkets so they must have it in stock somewhere.
I tried to cut down on soy sauce at one point as it is rich in omega-6 although it is supposed to be pretty well zero salicylate. However it puts a lot of taste back into the cooking and if the meal is zero or near zero salicylate does not seem to cause problems.