Both US and Japan.
Probably very few. The offspring are still a mixture of black fry and white fry. However, the juveniles from black fry must be grown for
much longer before their potential is revealed. I suspect most breeders just cull these instead of waiting on them. In koi breeding, time is money and space is money. You have to cull unacceptable fish as quickly as possible in order to make room for the good stuff.
Kindai have more striking colors. Kindai are less expensive to produce. Kindai are easier to market. Kindai are difficult to differentiate from a sanke. Real showa are a victim of identity theft and raising showa from black fry is a lost art.
-ste veho