You are a big boy Lloyd, finding a used one to fit would be tough. But, you are a lefty, and the typical R and V safeties, over on the left, worked pretty dang good for me when I was a lefty. I imagine, if you took some time to wrap your head around it, a Greener left safety would work just fine for you.
That said, I started with a Darne when I was in my 20s, when most of my peers were graduating from a single shot that came from their folks, to an autoloader, that came from getting a full time job. Nobody could figure out why I wanted one of those old double guns, especially one like a Darne. I’ve been at it, a long time.
It isn’t just a Darne that gets you heavy barrels with a high level of proof in French guns. The run-of-the-mill boxlocks are typically stout as hell. Ammunition just isn’t an issue.
Best,
Ted