Simple frequency-tunable spark generator?
I am attempting to design a steampunk / gothic horror-styled electric harpsichord, with sparkgaps as the sound source in the vein of musical Tesla coils.


The device you are describing is, functionally, very similar to a spark-gap radio transmitter. The use of these devices has been banned by international law (!) since the 1930s, as they produce wide-band radio interference.

Unless you have a specific, detailed plan in mind for preventing this device from producing radio interference and confirming that its emissions are negligible, I would recommend that you consider alternative effects, or a simulation of a spark gap. The potential for a device like this to cause havoc by (e.g.) interfering with public safety radio systems is too great.