@Len, delivery is estimated at 2-4 weeks.
@Scott, I did consider geting one made but reckoned it would cost about the same.
@scrappile. I checked and it is 3/16th UNF thread. I have a bolt as a temporary fix but it doesn't have the nice soft rounded end of the brass original so will likely wear the surface it bears on.
Ultimately I reckon I will bite the bullet and order an EX21 but I am being quoted a 2-3 months lead time on one of those.
Rob