I do not know what is the most practical way of getting Po-210. One
possibility, according to the nuclear chart on my wall, is to bombard
Pb-208 with alpha particles to form the Po-212 compound at just enough
energy to emit two neutrons. Then you must separate Po from the Pb in
your target by doing some chemistry. The other way is to count on long
desintegration chains taking place in the spent reactor fuel.