I found the exact fish I wanted at a specialty fish store today. They build custom aquariums for businesses and people who have more money than sense. It's located south of Pittsburgh, PA and east of Washington, PA. The store is called Wet Pets.
I found a black ranchu with a nice wen. It had a faint orange tint to it's underside but otherwise it was a nice black. It was about the size of a lemon. They wanted $100.00 for it. Sadly, I left it there.
How much are fish where you live?