Most toggle switches mount in a small round hole which can be made with drill motor and bit. Your switch should be wired to your power source, so that when the switch is off, all power to the system is shut down. Many parts, especially motor drivers, have a nasty problem where feedback through various ground paths can cause them to engage. The last thing you want is for your motors to turn on at an unexpected time. Switching the power from the positive lead from your power source is a good way to ensure that this doesn't happen.
New switches are, to be honest, ridiculously expensive.
However, the surplus market is full of decent switches for a reasonable price. Electronic Goldmine or All Electronics usually have a good assortment of switches available. Vetco in Bellevue, WA is also a place to find them on the cheap. A handful of these will last you a while, and you will find that your projects will be easier to deal with. Send me mail and ask away.