Does anyone know where to purchase a spindle hub die (2.125 in x 24 threads /in ) ?
A much lower cost tool would be the thread chaser file. It comes with several different thread pitches on it. I am guessing this is what you are looking for, to clean up the hub cap threads.
My hub caps a steel and chrome plated (I know they should be nickel). One of my hubs was buggered a bit, but I didn't have the die to fix it with. I used an old trick my dad taught me. I took one of the hub caps and using a triangle file, filed three grooves evenly spaced through the threads of the cap. I then threaded it onto my buggered hub and used it like a die, turning it 1/4 turn, backing off 1 turn and repeating until it threaded on past the buggered area.
I still use that cap on my car, nothing wrong with it...it's just got an extra function now just in case I need it again.