Mark S.
I think you assume that all subatomic particles such as electrons must come from atoms. There are lots of free subatomic particles available. A good example is the solar wind from the sun. Another is the decomposition of radioactive elements, which cause the emission of subatomic particles. If you energize a large capacitor, one plate will have a huge excess of electrons, and the other plate a huge deficiency. The total net charge will be zero. This unbalanced state will hold forever, unless there is a leakage between the plates. If you can totally isolate a bunch of electrons somewhere, they will have no place to go, and will remain in that state forever. If they have physical contact with a material such as air, they will disperse and dissipate until they find an opposite charge somewhere and neutralize.
Ratch