Elgato just released the Eve Light Switch, a HomeKit - enabled Bluetooth LE single pole switch that'll run you $ 49.95. (imore.com)
Thinking of your wiring description, it is also possible the key switch is double pole, not single pole as in the circuit diagram, hence the black / white wires going to it. (mechanics.stackexchange.com)
Also I have wired hanging lights and drop ceiling lights and I have wired multiple types of light switches from regular single poles to dimmer light switches. (livecareer.com)