Looking to generate 25 Hz square wave at about 90 V AC
Sounds similar to a telephone ring tone generator, for example like this one, based on the LT1684: 



The LT1684 is a more complex chip that actually generates a PWM sinusoidal wave. 

Generating a square wave is easier, you can just use four MOSFETs or IGBTs and bootstrapped MOSFET gate drivers (eg. from IR). A full H-bridge with ~ +95VDC supply can be used. 

Depending on the MOSFETs you can drive 100mA or 20A with a similar circuit.