I dont know much about lefty pistols, but you will most likely have to special order it, if the manufacturer of the gun you want does such a thing.
You have lots of choices in .40 and .45. Likes, dislikes? Do you like glock, or hate them? Glock makes pistols in small sizes with big calibers. I dont really know of anything else that is bigger than a 9mm, but still small enough for ccw.
Hope this helps.
Joey
P.S. I just bought a sig p232 in .380 (9mm kurz). Its designed for concealed carry, I love it. I dont know if it can be had in a left handed model. You should go to the Scottsdale gun club and talk to one of the guys there. They will special order anything without hassle and know what is available.