Where can I get a transformer (electronics)

You can buy transformers at electrical supply houses. Radio Shack may have some. If you want to learn about electrical engineering, tearing apart old AC-DC power supplies (chargers for cordless phones, iPods, electric razors, etc will provide you with coils of various sizes. If you have a volt meter, you can experiment.

An audio transformer probably won't work, it likely doesn't have the step-up ratio you need.

Try applying a pulsed voltage to the secondary of a transformer out of a low-voltage modular supply, that is, to the low-voltage side and see what you get out of the 120 volt side. The lowest voltage supply you can find should give you a good spike out its primary. IOW, you'd be operating the transformer in "reverse" and applying only voltages < ~ 12 volts to it.

If you can't pulse (i.e. chop up) the input voltage using electronics, you can use a cheap buzzer to create the transients you need to run through a transformer (DC won't work).