The team of GameTextures.com has recently launched the largest library of Physically Based Blender Format materials ever created.
The update to their products is said to be free and apply retroactively. If you have downloaded any of the team’s products, you now have access to the Blender format version. Follow this tutorial to get started.
The process here is simple: just find the perfect material for your scene, select the download option, and then scroll until you find Blender. For the full tutorial follow this link.
GameTextures.com also has tons of procedural substances on the internet: thousands of drag-and-drop Substances and more. You can learn more here.