• This list of Project Gutenberg content has a ton of older stuff from great authors
• Year’s Best Science Fiction is a great starting point to find good authors
• This SF Encyclopedia article has basically everything on anthologies so it’s a good place to branch out from

Libraries and book stores usually have anthology sections. Once you find an author you like, you can usually find more of their shorts. As a kid I always bought a ton at used book stores. With more modern stuff (00s and forward) you can usually find a lot of it online once you know the authors you like. The collection you read has a nice range of styles so you’ve got lots to experiment with it!