SD,
The dealers will occasionally have a left handed item from a well known maker. The problem both for us and for them, is that it probably isn't exactly the maker/model/knife/options you would want. I once ordered a lefty knife through a dealer. In the process I deal both with the maker and the dealer which was nice, because I was able to build a relationship with both.
Also some makers bring lefty knives to shows. The problem is the same though, if it's not the exact knife you want, or doesn't strike your fancy the knifemaker has a knife that may be hard to sell. In general I like to go to shows and build a relationship with a maker and place an order for exactly what I want. The wait is painful, but as they say, "pain is pleasure" and when the knife does arrive I appreciate it not just for the knife, but for interactions I had with the maker and other folks on the path to getting it.
There are makers who are on the forums whom I've never had a chance to meet at a show nor seen their work in person. This is tough, because you don't really know if the knife is as good as the pics and other people say they are. This is where a little bit of a gamble, some faith and a lot of research come in. My lastest example of this is Michael Cooper's Cajun. Haven't ever seen his work in person, and some of his pics are a little fuzzy. In chatting with him on IRC and in email he seemed like a good guy whose work I wanted to see. So I ordered one and months later get it - I'm very happy with the result.
Ordering without having seen the knife in person is a double edged blade though. I've ordered knives who lots of people hype on the forums and are probably genuinely excited about. When I recieve some of these knives it's a big letdown. Poor fit/finish, sharp corneers, etc. I just chalk these up as the cost of education and move on
Also realize that if a maker is really popular and can sellout without problem, there is little incentive for him/her to make lefty knives at all, because in all truth it takes a little longer (mental strain) and they likely wouldn't want to charge more for it. Bummer, but that's the way it goes sometimes.
~Mitch