Update after checking various website and a few phone calls I could not source a 3v bulb so I followed MichaelG suggestion and fitted a LED soldered it onto the base of the old bulb have to say it much brighter than the 3v bulb. Thanks for all the info.
And far too late I just recalled an old surgical system i found 40+ years ago that was illuminated by a tiny bulb from 'the chicago miniature lightbulb company'… and google tells me they are still about…