Do you mean a voltage doubler, Ken? T'is a simple circuit but, why not just use '12 volt' steppers? They're very cheap.
Rob,Stepper driver kits are also avail & cheap from u know who. Try Oatley Electronics/D.Smith etc etc. L.
As avandonk said, steppers don't really have an operational voltage. It depends on how you control them. My big box of steppers are all 1.8 deg/step and the listed voltages range from 3.6 to 9.4. All motors came from copiers that have supply rails of 5 & 24VDC.
The one on my desk is listed at 4.2V & 1.5amps, weighs in at 600g. These are fairly typical motors to salvage from copiers.
Ta Mick/Michael. Wasn't too sure re; applied voltages. All the circuits I've come across have been run on 5/12 volts only for the 'ease of access/simplicity/cost' factors, ie; batteries/plug packs. Should have looked more closely @ the circuit I posted. It shows/states you can apply up to 35 volts to the steppers....... L.