Owen,
A couple of weeks ago at the Beaulieu Autojumble I spoke to a chap called Keith Ardley who runs a reflector re-silvering service. I have his card, he charges £5 per 1" measured across the diameter of any brass reflector (this is what is written on his card) his contact details - 14 bridge Road, Mepal Ely, Cambridgeshire, CB6 2AR Tel 01353 778493 email
keithardley7@gmail.com
I have no connection with this service but what he had displayed on his stall looked very good. Though he does not do it himself he can also get mirror glass re-silvered for about £25 each.