If you need a sinusoidal output then most small audio power amps are capable of 100kHz if you adjust the deliberate high-frequency roll-off point. If you need a square wave then the harmonic frequencies required will be over 1 MHz, which is beyond the reach of most audio amps. You haven't provided sufficient information to answer your question.
In addition to all the many other possible solutions, one could also build a simple Class A amplifier using a power FET as the active element. Neither 100 kHz nor 1 watt is challenging. Dead bug construction and adjustable PS, bias and drive. It should be straightforward.
