Several years ago, maybe 10-14 years, I could send a lens element to Arax in Ukraine and he had some “contacts” at the Arsenal factory and he could get the element polished and recoated very reasonably. Is there any such place today? I’m in the USA..
There are a number of companies you could try that specialize in lens and mirror coatings. I would start with AccuCoat in Rochester, NY and see what they say.