https://en.wikipedia.org/wiki/Garum#Legacy
Example: Tiparos (on the left) https://importfood.com/products/thai-sauces-condiments/item/...
Happens I can recommend tiparos as it's not brutally salty like others I've met. My guess is that this modern kind of fish sauce is useful (and I've heard it highly spoken of by a semi-professional chef) because it's high in glutamates which taste meaty (umami) but that's just a guess.
It is true however that there are still Italian and Greek garum producers, as I mentioned, who claim to have been producing since Antiquity. Though this is 100% unverifiable, there's little reason to think it's not true. The thing about garum production is that IT IS SMELLY! Very, very smelly. Roman law actually forbade garum production within a certain distance to the city walls. And as the Western Empire began to evaporate, the production of most specialty / delicacy items (think wine, garum, honey, cheese, etc) moved to "wealthy manor homes" which -- because of the danger of the roads -- slowly became the armed fortress fiefdoms of feudal Europe. So probably it just fell out of favor as time wore on, except in a small few exceptional places.
The UK is on your side of the Atlantic, unless you go the long way round of course.
Edit: I get it, they matched it to the New York example.
I’m not surprised they ended up finding the only known example across the Atlantic - Bulgaria has great, completely empty, museums - this was one of many where the surprised attendant unlocked the place so we could go in.