Hello,
Substance Source is an ever-growing content library where you can find physically based, high resolution and tweakable assets for texturing. From fully procedural materials to physically based scans and hand-painted materials, Substance Source is the place to find assets suited to any type of 3D project. Substance can be used directly in UE4 using the Substance plugin. Download materials every month with the Substance Live monthly payment plan, or make a one-time purchase of Substance Source access (includes 12 months of updates).
https://www.allegorithmic.com/products/substance-source
Cheers,