So, I have raided my friends car shop for parts and I have found useful stuff.
How to make the bulb base:
there are several options that I played with:
1. Using crimp connectors and cut them in half. I used the blue one with a finish washer and threaded the LED through it. Painted it with faux brass - looks okay.
2. I used a wired bulb with base from HobbyLobby and half a green connector (without the metal squeezy part). Same as above, although I will get a bigger finish washer for that bulb base.
While these fixtures need more finishing, I intentionally left them as they are so that you can see what is what.
These two variations definitely look promising, however, I did not like them for the dome lights I have in mind.