For a one-shot story, I hunt specifically on digital platforms that allow you to filter by 'Single Title' or 'Standalone.' Many Kindle categories hide a ton of gems under 'Collections' that are actually anthologies of different authors, each telling a complete tale in 30 pages. I've found that smaller, independent presses often publish themed anthologies—like 'Gothic Blue Books' or 'Apex's World Jumpers'—where every entry is self-contained. The key is ignoring the big, flashy series banners and digging into the 'Also Bought' lists for books that are slim, under 150 pages.
Audiobook services are surprisingly good for this, too. Apps like Scribd or even Audible's 'Short Story' category feature narratives that wrap up in a single listen, perfect for a commute. I look for narrators I enjoy and see if they've done any solo performances of shorter works. Sometimes a prolific narrator will have a whole catalog of one-offs from different authors that you'd never find otherwise.
My final, slightly sneaky trick is to search for award nominees in the 'Novelette' and 'Short Story' categories—think Hugo or Nebula awards. Those pieces are almost always published as standalone works first, even if they're later collected. You get a curated list of high-quality, complete stories without any 'To Be Continued' hanging over you. I've discovered some of my favorite authors this way, simply because I sampled their skill in a compact format before diving into their longer series.