Radium from clock-fingers.
Radium is much more effective than Americium. Radium was used into around 1950, in clocks and watches, then it was withdrawn because it was too dangerous. The isotope Ra-226, an α-emitter, with a half-life of 1 599 years. It is hightly toxic and decays into Radon.
It was used to paint fingers and faces on the clocks, to get it self-lightning. But there are many clocks still. I bought a lot of clock-fingers on eBay. It's not so expensive, about $ 12 for 5 pieces.