18 Rock Brushes for Blender

I doubt the instructions for installation still work for modern Blender versions, I'd recommend just taking the raw textures and importing them manually. You should be able to create a brush asset using the asset browser for each texture.

18 Brushes to sculpt rocks in Blender.

This is not an add-on, but brushes that you append to your Blend file. More detailed instructions in files.

Hope you enjoy!