LH cone for Shimano HB-NX50 hub

I realise this is somewhat of a long-shot, but:

Does anyone know where I might get hold of a M10*~11.94mm cone intended
for use with 10*3/16" balls. The original Shimano part number is
Y-22V*03100 and the OD is 17.40mm (but cup would allow up to 23.60mm
without dust cap). Several official spares distributors' databases
claimed to have them in their just-in-time supply chains, but attempts
to order one elicited the response that none have been available in the
UK for some time. Newer Shimano hub dynamos seem to have wider axles/
shorter cones/ different bearings and therefore don't appear a likely
source for functional equivalents. Surprise, surprise.

I have put in a generic rear RH cone of very similar dimensions for now
(Ultegra freehub FH-6401/2). This is really for use with 1/4" balls.
It has held up well for a trip to the South of France and a couple of
thousand kilometres since, but I would like to lay my hands on a closer
replacement, if possible. Any help much appreciated.

--
Mark