Bookstores are also a great place. There are often bookshelves dedicated to Spanish literature. You can ask the staff for recommendations on short story collections. They might be able to point you to popular authors or anthologies that are well - received in the Spanish - speaking world.
You can find short Spanish stories in libraries. Most libraries have a section dedicated to Spanish literature where you can find collections of short stories. Some of these collections are specifically for beginners and have simple language.