Websites where you can find short stories.

Classic Shorts – http://www.classicshorts.com/index.shtml
Lots of classic popular short stories that are all in the public domain.

American Short Stories for High School Students: https://americanliterature.com/high-school-short-stories

Short stories for Middle School https://www.weareteachers.com/best-short-stories-for-middle-schoolers/

Links to a lot of Short Story websites: http://www.classicshorts.com/links.html