In my part of the world, we normally assume Sakai of Hiroshima when we hear the word Sakai. I know of Toshio Sakai and his work, but what actually is the name of his koi farm? Some writings suggest Isawa Koi Farm whilst some others suggest Yamamatsu Koi Farm (his brother's, I believe).
This link
breeders lists many well-known breeders (out of over 1,000, I believe) in Japan. I think the Sakai listed there refers to Sakai of Hiroshima. There doesn't appear to be any listing for Toshio Sakai, although Yamamatsu is mentioned.
Again, pardon my ignorance..