Given the small amount of current produced, maybe go to a series regulator instead of a shunt type? It reduces heat production in both the stator and the regulator, and also doesn't mind jump-starting, which I suspect is responsible for frying lots of shunt type regulators. I'm trying to think of other 24V magneto generator applications and can't come up with anything other than the small MEP gensets. The good news is that the right sort of design could be universal - deal with 1, 2, or 3 phase stators up to, say, 15 amps.