Ha, I know.
I have since found somebody who has them. Unfortunately, the entire mechanism is shown on the diagram
as one part number. They have no part numbers separately marked for drivers or anything else.
I went through this with Kato USA once, getting a replacement gear cover plate for a Mikado. It has no separate orderable
part number. But it DOES have an "internal" number because of course, Kato has to keep track of every part
in the model. They just don't make it possible to order those parts.
Oh well. I have my answer. We can't order drivers for those engines as separate items.