If you're trying to track down Hazel Warren's original short story, my instinct is always to start with the boring-but-effective detective work that actually pays off more than you'd think. First, I check whether the author has an official page or a publisher listing—small-press writers often have a note about where a story first appeared (a magazine, anthology, or chapbook). If that doesn't pan out, I run the title through WorldCat to see which libraries hold it; WorldCat will often point to the exact anthology or journal and the nearest library that has a copy. For older or out-of-print pieces, the British Library, Library of Congress, or national-library catalogs are surprisingly useful.
If I still can't find a readable copy, I look at digitized archives: Google Books previews, Internet Archive, HathiTrust, and magazine back-issue archives. Some literary magazines have digitized runs online, and Internet Archive sometimes hosts entire issues that include short stories (respect copyright rules, of course). If it’s a super obscure zine piece, I also check secondhand-book sites like AbeBooks and Alibris or smaller rare-book sellers; they often list anthologies or chapbooks that include the story. Reaching out via polite email or a DM to the publisher or the author (if contactable) has gotten me scans or straight directions before. In short, library catalogs, archival sites, and secondhand sellers are my trifecta—happy sleuthing, and I hope you find that piece; it's a lovely thrill when a hard-to-find story finally turns up for me.