Hi
This is a long shot but I can only try. Please read the text below.

I bought just recently a gorgeous pen. Unfortunately the nib and the nib section are not how I would have designed them my self, probably not even original. The nib is too small (7.25 mm wide, 18.50 long (visible part)) for this large pen (14 cm when capped, large girth, diameter 13 mm). On top of this the pen needs non standard cartridges.

Now I am looking for a new nib - section assembly that fits on a standard cartridge. Of course there are some other "interface" constraints. Most importantly, the thread of the section shaft is about 4 mm long with 4 revolutions, and spaced about 1.1 mm from the visible part (see pic). The outer diameter of this thread is about 9.77 mm. The barrel(on the thread for the cap) is 12.20 mm in diameter
I can re-thread the nib section shaft of a given replacement section on conditon that the shaft is thick enough (> 10 mm)
I think the nib should be at least 20 mm long and 8.50 wide, from steel alloy or gold .. and the section preferably should be black plastic or from metal taking standard cartridges.

See pic... so if you have something that comes near my description let me know !
Thanks for reading