Thank heaven for Google. I'd fortuitously just finished reading the biography of a WW II era occultist (W. G. Gray), and then picked up the war era letters of Dion Fortune (The Magical Battle for Britain) which were basically instructions for coordinated magical workings which she sent out to anyone who expressed an interest during the early years of the war.

Then it was just a matter of getting a few details like an appropriate SOE location, a model of gun, and a motorcycle.