Remington makes/made model 1100's and 870's for southpaws at one time. I picked up an 870. Not as many barrel choices, so I had it cut to 21" and screw in chokes installed. Works for everything that flys, and also works well for SD. It's pretty easy to install and remove the mag extention.
Remington, also, makes the 700 for southpaws. Again, not as many choices as for righies, but at one time, they were pretty much the only game in town for mass produced rifles. Mines in 30-06. Pretty much will do for anything on this continent.
Weatherby makes some fine southpaw guns. Priced accordingly.