Unfortunately, this is the sort of thing that can happen when companies get swallowed up by one of the Big Boys.
Meanwhile, these days it seems that UK companies who offer ophthalmoscope repairs specialize in Keeler. So perhaps that may give food for thought when or if you buy any new ones.
You could also have a go yourself, of course. It's usually just a matter of a bench magnifying lamp, some fine tools - and cleaning of delicate components (small lenses, and what-have-you).