I'm reading a book of Hemingway short stories. Some of the best ones IMO are some of the very shortest - not much more than a few pages long in some cases. I was curious - where would stories like this have originally been published before ending up as a collection published in one book? If people are writing short stories today (I'm aware of things like magazines specialising in genre-fiction - sci-fi/fantasy etc) - but people writing "general" short stories - especially very short ones - where do these generally get sold to before (potentially) ending up in a collection of short stories published by a successful author?
Take a look at Duotrope. When I joined, I was stunned by the number of markets for all kinds of short fiction, including literary fiction. Hemingway had the advantage of living in a time when all the mass-market magazines published fiction. Most of them are gone, but we have the internet.
Those very short stories were often called "short shorts" in the days of antiquity, but today the term "flash fiction" is much more common. Definitions vary, but it generally refers to stories of up to 1,000 words. Even shorter pieces may be called microfiction, and stories of exactly 100 words are known as drabbles. Whatever you call them, there are plenty of markets for them. Nearly every literary magazine accepts flash these days in addition to longer stories, and there are plenty of publications that specialize in flash or micro, mostly online. Among the bigger names are Smokelong Quarterly, Electric Literature, Wigleaf, and Daily Science Fiction. Like @Earp said, Duotrope is a great tool for finding markets for your work. I also use the Submission Grinder, which seems to have better data for small SF markets. And you can always just google "flash fiction" and see what turns up. Good luck!