If yours are the originals, then the reflectors are past their sell by date probably. You could put the biggest bulb you could find in there, and, with tarnished reflectors you are peeing in the wind. As Ray said, you could maybe find someone in the UK to re-chrome/silver them. The expensive alternative is new headlight assemblies.
Jaymic used to have them as I bought a pair a several years ago from them, (serious coin) but not shown on their website now.
Linwar, however, do show them.
https://www.linwar.com/bmw_e10_lights.html
Good luck whichever way you go.