The best way to get the various Japanese alloys is to make them yourself. This is one method I use which works very well for Shakudo and fine silver ingots. In this technique I use an electric melter with a steel ingot mould.
In this series of pictures below you can see the Gold, Silver, and Copper that has been measured out. This will be melted and mixed together to create one pound ingot of shakudo alloy.
The steel mould is prepared by heating it with a torch. Its then covered with a fine layer of candle black (soot). After the mould is assembled and the melt comes up to temperature the metal is poured through a specially designed charcoal funnel. This funnel distributes the metal through a series of holes rather than just one. This produces an ingot with much more uniform grain structure and nearly eliminates any shrinkage cavity issues. Shakudo is very prone to shrinkage cavities. After the ingot is cast it is broken down into plate and sheet stock. An ingot like this can yield a pair of Tsuba with lots of little scraps left for inlays.