Other than beta titanium alloy, which basically only Mecha uses for swords, there's not really anything suitable for sword blades that will not rust. A modern super tool steel like CPM3V will be somewhat stain and rust resistant as well as tough and keeping a good edge. But I am thinking it will be hard to make a wariha tetsu-construction blade with a particle metallurgy steel core. The people who would make such a steel are typically specialty steel manufacturers like Nichols Damascus, and that's seldom the same people who make traditionally constructed Japanese swords.
Even if you could find these materials and someone willing to make it, honestly this would be thousands and thousands of dollars for relatively small gain over one made with carbon steel.
