Hey Jeffery,
I don't have a source and couldn't find one, but when one of mine went out it turned out to be the switch on the fixture itself. I couldn't find a replacement switch that would snap into the old switch's spot, so I cannibalized the switch off of the cockpit light. I hardwired the cockpit light, figuring that any time I was going to turn on the side deck lights I'd turn on the cockpit as well, but not vicea-versa.
Not a perfect solution, but it works...if it is the switch.
You also might be able to convert it to LED with no ballast. I'm thinking of doing that to mine.