Is it a question of popping into one of the dealers like J&S in Watford?
I was a little enthusiastic tightening up a retaining screw on whatever the thing is called that holds the visor and it sheered.

Small black plastic fits into this hole.

Doh!, just thought to take a piccie of the other side

Not wonderfully robust construction, and a bit fiddly but it's lasted five years until I became interested in it.
Any tips gratefully received.