The easyest way to wire in a key switch is to ground out the coil. Or to wire in a key switch to the cable(s) before the on off button on the handlebars. And the cheapest way to get a key switch is to get one from ebay. You can get them there for 2-5$ with 4 cables. Got 3 of them on some of my bikes. 2 cables to the to the on/off button and 2 cables to ground out the coil. Dont know where you live, but here in Norway the most comen 125cc bike(for 16-18 year old kids) is the Husqvarna wr, smr or sms. And they get partet out all the time. You could get a used side stand for dirt cheap and they fit an the big bore Husqvarna's.