Check out this site! ambientcg.com This guy has 1300 textures, some photoscanned, some made with substance, and they are all CC0 license. Definitely worth looking at if you need a texture. He used to be called CC0 textures. He also includes the substance files.
Edit: Just read your question more carefully, this guy mostly has textures for models, but he does have a few rocks and other 3d scans, either way a good resource.