Charc, is the socket in your radial ERSs that you think is a screwbase actually a medium prefocus? If so, you have many lamps from which to choose. Once you post the pictures, I'm sure someone will identify them, then we'll tell you the lamp we used to use, and ship will come up with the preferred modern variety.
I'll go grab some pics before Meeting.
(Meeting? What's meeting you say?! Meeting for Worship. Part of the quaker religion. I go to a friends school. Essentially we nap in silence for 45 minutes. Look it up.)