Have a look in the cupboard under the stove and either side, if you find a 9V battery taped in there, then that is most likely the power supply.
The igniter takes bugger all power, just bumps up the voltage to get a nice fat spark and I'd think that the supply power from that battery is going through the switch, rather than having the coil energized all the time. A store bought switch should be able to handle it.
I'd took at Jaycar though, more range of momentary switches there.
If its 240V and wired into the wall, then Jaycar are also a good bet as they will have stuff rated to that, but I wouldn't be messing with it.