Nigel, are you looking for the cast pieces that clamp on to the crossbar or the cups that sit on the cast mount onto which the headlamps mount? If the latter, I have seen these for sale from one of the generic parts dealers, but I'll have to search again to find them.
Nigel, I think you will be lucky to find any, I advertised/looked for over a year and found nothing. Try Andy King, he had some recast I do not know if he has any left. That is where I ended up getting mine. Good luck