Im a lefty too, so i know the feeling, although things seem to be getting better over the last couple of years. They usually never have a left handed model to shoot in the store unless they let you shoot one they have in stock. What i do most of the time is shoot them right-handed. Granted its not the same, but i have gotten pretty good at it. But if you shoot a bunch of right handed bows in a row, it can show you the differences that you can feel, granted its not the same, but it does help and makes you a more versitile archer. And as others have said most of the shops are very willing to work with you to sell you a bow. I would go on to the bow companies you like websites and use there dealor locator function and go visit some shops. Some shops have better selection then most, but it does pay to shoot them all, or at least hold them.
Good luck