Finally, a source for these
"While updating a bathroom, I discovered that the thumbscrews securing glass shades in the two 13-year-old fixtures were corroded. I was able to make the chrome fixtures look good as new, but could not clean the thumbscrews. The fixture manufacturer told me these parts are obsolete. Local stores and electrical supply sources did not have them. After much searching online, I found Antique Lamp Supply, and they had just what I needed. These screws are a tiny bit longer than what I need, but that's fine. And although we measured the existing screws, the new ones turned out to be a tiny bit larger. But after using the appropriate tap tool, we successfully enlarged the screw holes in the fixture. Customer Service was very helpful in confirming that I had the most appropriate parts for the job. Coincidentally, ALP also had a replacement for an unusual kerosene lamp chimney that I broke years ago. I keep things forever, and now I have a source for replacement pieces and parts. Thank you!"