The parking bulb is a nice to have, but most people never bother using them as if left while parked, they will drain the battery. But, if you are determined to have one, keep an eye out for the original headlight for a VW bug from between 1950-1965, or there abouts. Most had the parking bulb socket in them back then. The originals took a 6 volt Tungsten bulb as the Quartz Halogen was not available then. But, they were often retrofited with 12 volt H4 bulbs as people converted the original Bugs to 12 volt.
Damn, I am really showing my age, with all this old stuff, from my ill spent youth, hopping up little cars (tuner cars?)way before it became cool.