Tancho do not form a single, independent kind of Nishikigoi; they all can be bred from Kohaku, Taisho Sankshoku, or Showa Sanshoku. Their red patch happens to show up only in the head region. Tancho, therefore, can not be produced in bulk even if you so wish.
The essential point for appreciation is the red patch in the head region, of course. The red head patch sitting right at the center of the head region is the best. The white skin is also important as it is the milky white color that sets the red head patch off to its advantage. The Sumi of Tancho Sanshoku and Tancho Showa are the same as Bekko and Shiro Utsuri respectively.