Diameter is common with 2CV round headlamps, and also Cibie Oscar additional lights, the latter sharing the lens, too. Both of them, however, lack the adjusters and spring clip tabs. I don't think there is a practical way for these items to be fitted, they are spot welded on the mirrors.
I have successfully rebuilt such corroded headlights, by unglueing the lens and having the mirrors rechromed.
There are a couple of companies here in France that offer a re-mirroring service (you send your headlight to them and, if the unit is not in too bad shape, they separate the lens and renew the mirrored surface). Perhaps something like that is in place in SA?
It can be cheaper to source a replacement item but when there are no replacements, or preserving originality is your goal, it's worth considering.
Hi Simon, thanks for the info. I actually spend 6 months of the year in Spain ( i dont do winter ) so can probably get them shipped to me there. In fact my motorhome is in storage at a friends in France so even easier. I plan to buy a R4 as a daily driver in Spain, there are still a lot about!