You'll need a high voltage, high current op amp, such as an audio power amplifier. Take a look at **broken link removed**. I haven't used it, but it looks like it should work. You will still need to generate a low voltage square wave to feed it. The first thing that comes to mind is a CMOS 555, either running off symmetrical +/- supplies, or off a single supply with an offset summed into the summing node of the op amp. If you need help with that, post your questions here.