what if I like doitsu showa longfins?

My bad, JR
The thing about ginrin is it is actually, in a greater sense, a pattern on the scales. To be clear, it is a scale type and not a pattern type. Yet, like a pattern, it will be predictable in that it will tend to show up on certain areas of the body and in certain concentrations in those areas.
When Yamakoshi village and surrounding areas tamed to some degree Niigata gin, they were actually organizing scale types that were 'speckled and widely distributed 'patterns' onto the back for top viewing. This is no different than organizing beni spots all over a white fish into the dorsal area only.
In the case of Matsunosuki sanke, I think it is best to think of ginrin as a linked trait like 'freckles on a red head'. If you want the silk skin and that skin's ability to luster and reflect light so it appears silvery white, then you have to accept that you will likely see ginrin in strips along the tail tube or body.
Kevan is right in that to buy a matsunosuke sanke TO get ginrin is not the point! And I have seen Mat.sanke that have the gin but no fukurin or silk to the skin. That makes no sense? Kinda like buying a porsche key chain but not the car? Or maybe a blank canvas signed by a famous artist?