I have a couple of glocks and they are great for lefties, at least for me. You can work the mag release with your middle finger (you might have to file it down a bit), I have no problems with operations. It's the most lefty friendly centerfire pistol I've found yet. D/A Revolvers are fine for lefties too. Browning HP's with ambi safety work great too. I think that some Heckler & Koch pistols come with controls set up for lefties if you order them that way. Someone else may chime in as I don't shoot them. Lefty UNFRIENDLY pistols include some .22 semi autos such as the Ruger and the Browning.
Holsters- try CompTac, you won't wait six weeks, just a few days.
Shotguns- Browning BPS (and other bottom loaders without crossbolt safeties) and Mossbergs are ambidextrous, as are doubles of course. I love my Mossberg. I have a left handed Remington 870 but I like the standard Mossberg better.
Also lever guns that predate the dreaded cross bolt safety are easy to use if you are left handed.
Lots of options.
AVESGUY