Disclaimer: possible duplicate of this question.
Considering what I read there, I would refrain from asking this, but a (english professor, british native speaker) colleague of mine's husband (off-topic but I'm a portuguese citizen) stated against it, so I would thank some further enlightenment.
He advocates "some" should be solely used referring to plural forms and thus whereas
"some non-existent towns"
is perfectly correct
"some non-existent town"
should be replaced by
"a non-existent town".