There is a need for heat in the parkerizing process. It is usually done in tanks just like hot bluing is done in.
Nonya, you might check out black wrinkle finish paint, you can get it at auto parts stores, Auto Zone, Schucks, etc. I have a synthetic stock on a used R77 I bought. It had scratches, scrapes, and a few gouges on the stocks finish. I stripped the old finish off with paint stripper, sanded it down with 180 grit wet dry paper and shot the paint on. It takes about three heavy wet coats, just follow directions on the can. So far, couple of years now it is holding up well. The only down side is the smell last for couple of weeks. This is because the solvents in the paint are evaporating slower due to the heavy multiple layers of paint.