Quora has some links in a similarly worded question that might provide further insight https://www.quora.com/What-is-the-best-website-for-free-game-art-assets-and-game-development-resources
Also, a Github repo with resources for indie game developers that includes graphics: GitHub - ellisonleao/magictools: 馃幃 A list of Game Development resources to make magic happen. 路 GitHub
And another: GitHub - DaRaFF/jsgamewiki: A collection of good links for gaming with javascript 路 GitHub