While browsing some Russian knives forum I've stumbled upon a post about selling natural Chinese sharpening stones named Guangxi.
Seller claim they have a grit around 12-15k.
While they are probably better used for sharpening razors then kitchen knives, seller writes that knives also benefit from those stones.
So I wonder if anyone here has any experience with such stones. Seller ask around 70$ including shipping and I wonder would it be worth it or not
I've also found a rather old review of those stones comparing them to Shapton Pro for finishing razors. It's in Russian but there are quite a lot of pictures, including magnified edge after sharpening, so it still might be useful.