For a 1951 3100.
Jim Carter has some listed for earlier models. I contacted them and was told they are out of '47-'54 and don't have anymore windings to do the conversion.
I tried an aftermarket 12v but they don't work. The needle presses on a shaft rather than being bent like the original. The hub of the needle hits the face glass. I don't know how anybody is making those work. I also tried resistors (several types) but was not having much luck with accuracy.
Seeing that JC used to sell them I thought maybe someone else does, or could convert my original.