This process was used to coat/treat cast iron cams to help retain oil and prevent scuffing during break-in. It was NOT used 100% at the OEM level but was used pretty much across the board for aftermarket cams. It ultimately did more to prevent corrosion than prevent scuffing. In fact, this is why the process was ultimately eliminated from lifter bottoms at one time.
The NASCAR people found that micropolishing did more to eliminate friction and reduce break in problems than zinc phos coating. It was also learned that a well formulated SF grade of engine oil, fortified with GM"s "Engine Oil Supplement" did a good job of eliminating the need to zinc phos coat cams.
NONE of the prototype cams we make anymore have/use the coating process.
However, if you have a salt spray corrosion test that you have to pass, you're probably going to have to find someone who can/will still do it. It is quite reactive with steel and not that environmentally friendly so it will be a PITA to find.
You might check some of the production engine rebuild shops as they still might do it or know who does it.