The one I put on my build, I got from rebel56 who got it from another member. 50s and 60s motorcycles had that large headlight in a metal base. When you start getting 70s and up, you will get into plastics, fiberglass and then composites...
One of many options ive done for lighting, I cut the back out of a sealed beam headlight and jb welded a 1057 automotive light socket ring into it, and went and picked up a couple super bright led 1057 bulbs. They can be powered with 10 hearing aid batteries, or 4 2032 wafers, or 8 aaa. Just gotta get to 12 volts. The batteries fit within the headlight housing. Leds use so little power they last awhile..
I have also added containers to hold the larger celled batteries before, back before LEDs gave us so many more options...