Hello parkisaac!
This is my first post - hope it goes well. I, too am a lefty looking for the same thing. I did find out that E.R. Shaw barrels will convert a left smooth bore to a rifled barrel. Basically, you send them a smooth bore left barrel - they strip it and add their barrel so you have the cost of the smooth bore plus $300.00 for the conversion. Stay in touch if you find anything else