I'm wondering if the method used to make the pentel pencil would work. I know it required a stepped drill bit that isnt available any more, but if you had a metal lathe, I think you could "reproduce" one. Essentially, take a piece of drill rod turned to about 1 thousandth under the larger drill bit for about 90%. The last bit would be the precise size of the larger drill bit and then would have the smaller drill bit set into the end.
It wouldn't even have to be that long, because you could drill it and make it in two parts. Essentially, the section would be step drilled for the pentel pencil refill. It would also be threaded m10x1 to fit into the body. The body would be drilled all the way through to accommodate the refill and have a hole at the end of it for the plunger.
If I get some time, I'll see if I can make one and see,if my idea is plausible.
