I have tried pinging the reeds with a guitar pickup, Tom. I’m skeptical about tuning in this way or by blowing air across the reeds, because of the extent to which where and how you blow into the instrument affects sound and tuner readings. For example, I get different readings (at the low end, at least) using a mouthpiece than I do blowing directly into the melodica, and also for the melodica in its shell and the melodica out of its shell. I haven’t experimented systematically with this. But I suspect that there are differences between “true” tuning of the reeds and tuning in relation to how it actually plays. It may even be that the melodica is best tuned relative to the particular player. Given the extent to which “Lowboy” technique involves so much manipulation of notes, it might be that “true” tuning is actually best for you. If my theory is right, though, absolute or true tuning of the reeds may not be a viable approach for melodica tuning in general. Alternatively, maybe I’m all wet on this.
I recently acquired an electric engraver that I plan to try using next time I do some tuning. http://www.amazon.com/gp/product/B0060C7PDM?psc=1&redirect=true&ref_=oh_aui_search_detailpage