Welcome to CC0 Textures!
Physically based rendering allows for incredibly realistic surfaces, but generating a good PBR texture is not easy:
You need to wait for good lighting conditions, go outside and shoot the textures, stitch the images together and create all the maps.
That's why texture sites exist, allowing you to quickly get all the textures you need. But most of the time there's a catch. You can't simply redistribute these textures from other sites as files. Let's just get rid of that limitation!
You can simply take all the textures on this site, include them in your project and distribute it however you like. You don't even need to give credit.