You can pick up the switch at any auto parts store. I think I paid about $10.00 for the switch from Auto Zone - it was a 12VDC racing toggle switch.
The bypass works well, though you really need to use it with caution - it will be very easy to break your front axle if you wind up your front tires, like in mud, and then they all of the sudden catch traction with one or both wheels, or you have the wheels turned and try to accelerate qiuckly on a good traction surface, etc...
I use the rear locker in some 2WD and 4WD High situations (Mud and Sand) and only use the front when absolutely neccessary - it gets unlocked immediately after use.
Good luck and use it sparingly if you decide to do it.