WHAT TYPE OF LIGHT? Aqua Signal, or??? Are you sure it's a corroded bulb holder or bad connection? I suggest you open up the light i) check that; and ii) then pull the bulb.
Assuming it's the the bulb, you should be able to order one if you know who's light fixture it is. Otherwise, I'd go to West Marine (or an auto parts store, or...) with the burn-out one, and say "give me two of these."
It's likely a simple incandescent bulb that you can get through the mail too.