Gumroad - https://gumroad.com/products/hRhuy/
10 High-quality 4096x4096px rocks alpha brushes.
10 16-BIT TIFFs and 10 8-bit PNGs are put in separate folders.
They are based on my own photogrammetry scans from this Fotoref reference pack - https://www.fotoref.com/products/porous-limestone-cliffs-1#3d-scan
If you want to learn how to bake them on your own check the videos :)