Have you tried Canadian Tire,.. you can use any tach that incorporates a signal wire that you can put around the coil wire. As long as its only a single spark you should be golden.
You could also find someone with a volt/ohm meter that has an inductive rpm clamp.
this is what i had on my yfz 450 until i rolled it and smashed it, works well i liked having it especially while i was jetting, and messing with my gearing.