I'm guessing that you're talking about semi-autos here. After all, most single action revolvers based on the Colt
are left handed guns, and double actions aren't available in mirror image form.
My wife, dad, father-in-law, and a couple of shooting buddies are all left handed, so I've been shopping for the same thing for years in rifles and semi auto handguns. Ambidextrous pistols are offered by most major gun makers. For example, a lefty that likes the CZ 75 can buy a CZ 85, which has controls on both sides. Other companies, like SIG and Heckler and Koch, have offered guns with controls swapped to the other side. Things are really pretty good for lefties right now, because lots of guns are pretty much ambidextrous from the start. Just pick a gun that interests you, and check the company's web site for ambidextrous/lefty friendly versions.
My dad just learned to shoot the 1911 without changing anything, because Uncle Sam didn't bother buying aftermarket parts for lefties. He pushes the mag release with his left index finger, and he releases the slide by pulling it back a little with his right hand and letting it snap forward to load. The safety is also disengaged with the weak hand. It's not ideal, but it can be done.
