You can find loads of videos of real women covering themselves in poo, but not really any porn of fictional characters doing that, and I want to see hentai like that! You get scat eating and things like that but that's not what I'm looking for! Does anyone know any artists who do that kind of thing? Or would you be inspired to do so?

No

The question was more for people who do know

Probably not very helpful, but I think the closest you'll find on here is characters naturally being covered in it due to, y'know, shitting their brains out. On someone's dick, on someone's ass, you get the picture. There might be a tag for what you're looking for, but to be honest, that's just a guess.