This is a paid asset, but now you can download Realistic Materials Pack #2 for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Realistic Materials Pack #2 v1.0
This pack contains 50 materials with 103 seamless textures ready to be used in your project.
This pack is suitable for any outdoor or indoor scenes in your project.
Texture Sizes: 2048x2048px
PBR Seamless Textures