Honestly, nobody. Check out the right hand models of guns at the store that are offered by manufacturers in left hand. Then order whatever you want online or through the store.
I'm, a righty myself, was asking for a friend. Think we'll take a trip tomorrow down to Houston Armory and maybe Collection. Neither of us has ever been. If all else fails, we can hit Gander Mountain.
Ruger was always good about making ambidextrous weapons. Honestly, the right handed gun thing never bothered me. For semi-autos I would use my index or middle finger to drop the mag. Use the index finger to release the slide stop, and index finger or thumb from supporting hand to activate de-cock lever or safety.
Now I shoot mostly revolvers again. There is not advantage/disadvantage for us lefties. One advantage, though, lefties use there strong hand to reload without having to turn the gun upside-down/inside out.
Well I went to purchase a left handed AR from a local gun shop today. Unfortunately it was already sold. I pretty much expected that so it didnt upset me too much. What got me was when I asked if they could get another one I got a sort of "one in a million" answer. Pathetic IMO. Not even a "let me check". I refuse to buy a right handed rifle again and now I guess instead of helping the local gun shop (which I'd rather do) ill be buying one from some internet dealer.