Singapore is a real Omelas situation, where the little boy is all the migrant workers that underpin society. (Of course, the same criticism can be leveled at the US as well.)
Every country is a real Omelas situation—I don't think we're meant to read it and go "man, sucks to have to make that choice," but, "oh, it's an allegory for the society I actually live in".
The entire global economy is one, too, in fact. Not to spoil it, but that's something The Good Place ends up wrestling with by the end.
