What’s the application? How do you know that you need something as hard as tenifer? What’s you plating thickness requirements? Specifications? Etc.?
The application is engine parts for Jaguars, which were originally “Tufftrided” which is another name for ferritic nitrocarburization aka Tennifer/Melonite/ etc.
Since these are intended to be top quality upgrades or replacements, these new parts need to have at least the same heat-treatment/coating as the original.
So far, we haven’t been able to find anyone in the US that can do the inline six crankshaft - but there’s plenty in England that can do it.