I'm sure none of the double rifle manufacturers has a problem making your gun left handed.
I bought a used Krieghoff. I sent it to them to change the stock to a left handed stock. They did it easily and the cost was relatively small. While they had the gun they turned the triggers out to the left making it a beauty to shoot left handed. The top tang still opens they regular way and it still shoots the right barrel first. To me it is my left handed double.