Changing the camera to a 12v DC unit would probably be the easiest / cheapest option.

Failing that, if there were a number of cameras and they were all cabled to a common power supply point, then I'd consider fitting a chunky 240vAC > 12v DC mains adaptor, and then use that to drive an inverter to bring the power back up to 240v AC 50Hz.

Be aware though that some inferior quality inverters don't produce a decent sinewave (it's often squarewave), and that may result in minor picture / stability problems with some cameras that need a nice healthy waveform as an absolute reference.

Years ago, in a similar situation it was actually quite simple to graft a small '555 timer' based reference board into a camera, but with modern surface mount circuitry, you really don't want to go there

The specs for that model indicate it supports sync of INT/Line Lock - so you should have a dip switch somewhere, or some means of changing from linelock (60hz) to internal, which I would assume would be 50hz?