I've seen a few resources floating around teacher forums and homeschooling sites, but 'The Blue People of Troublesome Creek' is an article, usually anthologized in textbooks or used as a standalone handout. The 'answer key' you're looking for would likely be tied to a specific publisher's worksheet or quiz. McDougal Littell's 'Elements of Literature' and Holt's collections have included it, so the key is probably a PDF created by a teacher who uses that text.
You might have luck on Teachers Pay Teachers if you search the exact title, but it’s not an official, widely distributed document. Honestly, the questions usually focus on autosomal recessive inheritance, the methemoglobinemia explanation, and the social isolation themes. I just made my own key based on the article's facts when I taught it last semester—took twenty minutes. The printable versions are really just those worksheet PDFs, not a separate answer key booklet.