An interesting idea, I expect that you will get some kind of resonance as you hope. One of the mechanisms for this might well be the formation and subsequent escape of gas or (depending on current and voltage) steam bubbles from the gap. Not sure you need a neutral plate btw -I think it will merely confuse things by producing 2 resonant systems rather than one. What you have is akin to a tuning fork of course.
As for electrodes, I suggest you go to a cheap hardware store and buy a couple of cheap and flimsy stainless steel knives - they might be flexible enough to give you a result.