Genetically, it will be very difficult to get showa from sanke + kohaku. Sanke sumi is not the same as showa sumi, and the patterns that have been developed for the sanke, mostly stepping stones on the top of the body, are different than the wrapping type sumi patterns of the showa. Not saying it is impossible, as the breeds all started with brown carp and developed along the way to the fine art that we see today, so many of the fry are throw backs to previous genetics and out of that, you might get one. Chances may be about as good as winning the lottery, but someone has to win.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard