I suggest you provide the make and year of the motor, there may even be someone local on this board who has a spare or can point you to a good supplier.
Reminds me of once in college when I broke down on the NJ Turnpike in an old TR-4 with a bad ignition coil. A half hour later another TR-4 pulled over in front of me, asked what was wrong, and then pulled a spare coil out of his trunk. I asked him what I owed him and he told me to carry a lot of eletrical spares (Lucas was known as the Prince of Darkness) and help the next TR-4 owner I saw on the shoulder. Works a bit the same here.
Chris Baltic 37 Brut