I believe that light, which is supposed to be on the left fender, is actually amber. (I'll have to look at mine to be sure). It is a flashing light, controlled by a switch in the cab. It is served as a warning light that is was a wrecker (this was engineered and entered production long before the army was using convoy lights and other rotating beacons on vehicles other than fire trucks).
Wreckers, being assigned to maintenance personnel, were/are subject to many more really nicely done modifications than the average cargo truck, because the personnel had the tools, equipment and resources to make them. My wrecker has had, among its many service mod, an identical second lamp added on the right (passenger's) side.
But, to answer the original question, sorry, don't have an extra one.
Regards,
David Doyle