Increasing current with constant voltage
A common way to increase drive output current is made with a fairly simple modification shown below: -

Resistor R is used to tie the BJT emitter to the negative rail and the output is taken directly from the emitter to drive a load connected to 0 volts. This class A amplifier will suffice in many cases but, depending on what the load actually is and what current is needed, more sophisticated drive circuits may be needed. The next step would be a class B amplifier: -

And, by the sounds of what load you are driving this might be sufficient. If you really were intent on keeping sinewave distortion to a minimum, you might choose the bias the two BJT bases and make a class AB amplifier.

Or, you may decide to go digital with a class D amplifier: -