Paul - Do they have brushes for Corel Painter over there, not just PS?
I ask because, as far as I know, Sam is right when he says,
"You will never be able to make a brush that acts like real paint being applied with a pallet knife." (at least in PS).
Although I must confess that I haven't checked in quite a while, Painter's brush algorithms appear to be fundamentally different from Photoshop's in that they allow paint to be pushed around, built up, etc., much more closely approximating real world paints than the simple repetition of the same image that you get if you drag a PS brush around. That's what I attempted to show in that little example I posted.
As far as I know (following a quick search), the only other software that *may* allow semi-realistic impasto effects are Procreate and ArtRage, but I have no personal experience with these, only Corel Painter. So, if DeviantArt only has brushes for PS, it's not going to help him very much.
Tom M