You might take one, feed it 240/60Hz, stand back and see
what happens. Some of the cheapo aquarium pumps, the
little solenoid hummer types, don't have much to go wrong.
Less so, going up in Hz (less inductor current) than down.
If you can obtain an inverter made for European uses, then
it will give you the right 50Hz. I think I've seen 220V ones
on eBay. Put a battery in between it and a decent charger,
and maybe that does it for you. Depending on the motors
you might, or might not need a sine wave inverter.
I would bet that somebody sells "frequency converters"
but I'd also bet you won't like the price. Being as they
will be roughly the same as the charger-battery-inverter
lineup, omitting the battery, but not enjoying nearly the
economies of scale that residential inverters do.