Here is something you can try. Go and find an everyday dimmer as used on household incandescent lamps. Drive the coil using the dimmer. Place a capacitor in series between the dimmer and the coil.
Along this design line. Experiment with the cap for the best effect.
Years ago I did this and used an old clear glass incandescent lamp bulb. I made a foil cap (household aluminum foil) and connected the HV to the cap I made. NOTE: The cap as I refer to it is just a top for the glass envelop of the bulb. Form the foil to the bulb top. Then connect ground to the filament leads. You get a lightening storm inside the glass envelope.
Needless to say use caution when working with mains wiring and the coil secondary.
Ron