As far as can be known, there were four vehicles in the Metal Man line as shown in each of the Accessory Set pictures on the Accessories page. Shown, in order, is a Police Helicopter for Sgt. Silver, a Saucer-like UFO Spaceship for Radon, a Military Jeep for Corporal Chrome and a NASA Space Rocket for Major Mercury.
The only two that are confirmed to definitely exist are Major Mercury's NASA 1 ship and Radon's UFO, both listed below.
Radon's UFO Major Mercury's NASA 1