I've gotten a Ricoh and an Ilford Sportslite flash gun through eBay. The Ricoh, helpfully, (kind of) had a battery still in it - an Ever Ready B122, (which also fits the Ilford, whose instruction book leaflet describes the battery as a hearing aid type).
The Ilford recommends a PF1 or PF5 bulb.
I went into Jacobs in town to see if they could point me in the right direction, but got only blank looks and a recommendation that I look on the internet. (Oh, really? The internet? I hadn't thought of that, because, clearly I'm a stupid old bastard.) I'm beginning to think as I become more determinedly retro I should avoid camera shops all-the-gether.
Anyhoo, the battery is quickly found at Small Battery Company. Bit pricey, but hopefully it'll last a while.
The bulbs are a little more elusive. I want PF1s for indoor black and white. Cress photo is an American site which has them - though they seem a bit pricey, (I love the way something selling a retro product uses young women in bikinis on its website - is that intentionally post-ironic, do you think?).
The flashbulb collection has some useful information; (notably, that nobody but Meggaflash are manufacturing flashbulbs anymore, and the likes of Cress photo therefore must be scouring the world for old stock).
So the bottom line is, using the old flashgun isn't going to be cheap or hassle free. Maybe, in due course, I need to find an electronic alternative, with a PC adaptor and cold fitting.