Replacement Horton grip screws and nuts

I have a secondhand Dick Horton grip for a 208s where the fastening screws no longer engage. There is a small metal insert in the hole in the right panel, and I'm not sure whether there is supposed to be a nut there inside the metal insert, or if the insert itself used to have threading that has now worn away.

A regular hex M3 nut will not fit in the hole without damaging the grip since the hole is exactly 6mm wide and the hex nut is 6mm between the flats but wider between the corners. I tried getting some round nuts but they also do not comfortably fit in the hole due to the presence of the insert - the hole is deep enough for the nut but the extra constriction from the insert means that the nut can only drop about halfway into the hole. And I don't think I have a way to remove that insert with the tools that I have without damaging the grips. The nuts were also the wrong pitch (0.5, I think the screw is 0.35) and I could not find another source for M3 round nuts of the correct pitch. McMaster-Carr has a slotted round nut that could work but it is only available in 0.5 pitch, and nothing else in their offerings has the right combination of dimensions and pitch.

Does anyone know of a source for the right replacement nut? Is Dick Horton's business still in operation and would he sell me the appropriate screws/nuts if asked? Alternately, any other suggestions for the easiest way to fix this? I figure if I can't find a really easy solution like just getting the right nut, I'd go the more time-consuming route and get a new M3-0.5 screw, cut it to the right length, somehow remove the metal insert currently in the right panel, and put the M3-0.5 round nut I already have into the hole.

Look at the last post.

https://www.bullseyeforum.net/t11075p175-dick-horton-match-grips-new-e-mail-address?highlight=Dick+Horton#186917