1st off. Have you tried to polish what is still there? Not sure what the grey base metal is, but, it might polish with a little Simichrome or soemthing like that. May be worth a try.
The best way would probably be to re-chrome. But, as previously stated I think you're going to find that unaffordable for just these parts unless they can be batched with a much larger job.
I'd probably opt for Bright Zinc. Can easily be done with an Eastwood Tin/Zinc (easier) or Caswell Zinc plating kit (better but involves more effort) at home.
Even the super simple Eastwood Tin/Zinc kit will polish up to a lovely shine. The problem is that you have to then clear coat that Tin/Zinc with something like Nyalic to keep it shiny. I used that Eastwood Tin/Zinc process on restoration on a 1964 Honda Dream for many fasteners that were unique and couldn't be obtained back in mid-90's. They still look great and have a nice shine. Not chrome, but definately silver, shiny and good looking.
https://www.eastwood.com/ew-electroplating-...m-tin-zinc.htmlEastwood used to sell Nyalic clear coat especially for use with that Tin/Zinc kit. Tractor Supply now sells it. I can vouch that the old stuff from the 90's hasn't yellowed. Haven't used it lately so not sure about modern formulation of Nyalic. Supposed to be good up to 350F which is probably plenty for fog lamp reflectors.
https://www.tractorsupply.com/tsc/product/n...ASABEgI6CPD_BwE