OK, I did a google search and found out what a P-K nail is. I figured McMaster-Carr would have every kind of hardware known to man, but aparently this is a surveyors' specialty item.
This should be explained in the Course Measurement Manual. I read it cover to cover and could make no sense of the nails aspect, so I just used concrete nails. Since you have to drive them in a couple of inches and they are skinnier, there is more potential for trouble.
Thanks for you kind words on my skid.