12v external plug on Coromal Caravan

Hi I bought a new Coromal Magnum van and optioned for the water proof external 12v plug,its black round,made of plastic, has 2 circular pins one larger than the other and a thread for the ring on the male plug to screw on to.
My problem is finding where I can purchase some extra male plugs to suite.
I have found a few web sites that sell similar but they are made of brass and are smaller,they are used in a lot of marine applications.
If any one can tell me where to purchase these plugs it would be greatly appreciated,cheers Dino.
P.S. I live in Perth.