I will go to Canadian Tire, here in Toronto ( they have a few of them here ), ask for that type of sensor, if not available, well I will build an inductive type ( a circle ferrite - a donut -( not from Tim Horton XD ) big enough to fit the spark plug cable , I try to find an open type ferrite( like a current meter )) , or a radio type ferrite, loop some enamel wires ( from discard TV yoke ), maybe 50 turn ??? to 100 turn ??? and a circuit to "pick-up" the signal and send to a 555 monostable ( to clean the signal ) and send to an Arduino to count and display RPM. Experiment is a must in this case. And I maybe do a program on a another Arduino to simulated a pulse - like an engine, sending through a opto-coupler, the receiver part connect to the other Arduino with the counter program to test the software.
That will be my setup.