Thanks HR!There's a collection of links here to get started with:
https://www.artrage.com/manuals/gett...brush-presets/
I'm not aware of any others... yet
Note: Boxy's brushes are paid, but they're very good and he puts a lot of effort into getting them right. He made a lot of the official brushes, including the one that gets praised a lot in this video, so his presets are well worth picking up.