The vast majority is 100% orange juice, either not from concentrate, or re-hydrated (sometimes claimed to be "artificial" because they also add orange juice zest or oils).

To go back to my original, I can find traditional balsamic in multiple major grocery stores in my city. It's very expensive for a usually tiny bottle, but if you want it it isn't terribly hard to find. You can buy it on Amazon any hour of the day. And if your standards aren't quite so high, balsamic vinegar of modena, usually with just two ingredients (grape must and white vinegar) can be found everywhere for little, tasting marginally different. Italy considers and regulates either of those as "real".

We see the same gatekeeping claims with parmigiano-reggiano: Someone avails themselves on the Kraft green "parmesan" and then tells everyone else about how they've never tasted the real thing, it's so exclusive, etc (but, of course, they have that one time). Never aware that the cheese aisle has big blocks of 100% real, certified, regulated, straight from the source Parmigiano-Reggiano. This same discussion is occurring regarding tomatoes, as if having eaten a ripe garden tomato is some exclusive experience (rather than completely banal and experienced by virtually everyone).