I've never tried it but at least in the USA there are kits available
https://angelgilding.com/ to silver glass, plastic and if I understand their videos almost anything else with an undercoat. I've no idea how the chemicals used would react to steel base of the reflector. I understood them to be able to silver either the traditional back face of glass (useful for redoing CMP mirrors) or the front face of opaque substrates (what I'm thinking of for reflectors). They also mention coating to avoid tarnishing. I don't know if the originals were coated but assume they must have been or they'd all be black by now. The company referenced does mention international air shipment as being possible but I assume there must be local sources with reduced hassle.