Emma, it's in a collection I bought recently on Amazon which includes all her shorts together with this and 'The Ballad of the Sad Cafe' which is also excellent and also a novella.
MoftheW is written in three parts (McCullers adapted it into a play and it has been filmed at least twice). I caught part of the 1952 film on TV years ago and was mesmerised by that, also, and was delighted to find that it started life as a short story/novella and that the writing held me at least as much as the film did.
I'm not surprised it's referenced so often, it's a small masterpiece.
The lesson I learned, re. story length, is that any kind of edifice can be designed and built, as long as the architect knows what he or she is doing.
<Added>You're welcome, Jem!
<Added>I should add that I still think many modern short stories are too long (and, sometimes, too short - I can't bear so-called 'flash fiction'
because not enough attention is given by some modern writers to the various elements that need that attention in a story, just rambling on and often not adding up to a satisfactory 'wholeness'.
<Added>inexplicable wink there