I'd be interested in finding a proper manufacturer for these, although I'm only a hobbyist myself. Apparently, "kinetic switch" and "self-powering remote control" seem common names for these. There are also piezoelectric ones, but that's a different approach (piezoelectric effect, instead of induction with a coil and a small permanent magnet). Anyway, "kinetic rf switch" seems to yield quite a few hits on the web, including places like ledbulbs.co.uk, which might or might not be a valid UK seller of such stuff –– I not sure as I non-UK hobbyist ––, which leads to brands like "Culina kinetic switches".
BigClive investigated some of the eBay ones way back, and indeed it is very difficult to find which ones are fakes and which ones real, so I don't think even eBay/BangGood/AliBaba etc. are reliable sources, even for a hobbyist looking for just one or two units:
If you find out which ones are reputable in UK and/or Europe, perhaps sold in reputable local brick-and-mortar stores, do let us know, please.
(Here in Finland, it is common for such specialist companies to not sell to private customers, as they only do business-to-business, and because of reasons, I'm not willing to set up a company even just on paper.)