Here you can find some stuff that is free for commercial use.
Photoshop Brush Coloring Styles
A package of photoshop styles I use for coloring various of brushes. This styles work best with a black background.
Affinity Brush Coloring Styles
Similar package like the one for photoshop. Be aware that at the time I wrote this page, Affinity had a bug when displaying the styles, They are actually loaded, but sometimes do not have any previews in the Styles view.
Here some free brushes for Affinity: