A few folks have now suggested checking faunaclassifieds and kingsnake marketplace, which I have done. Maybe its irrational of me, but I feel more comfortable buying a snake that I've seen in person. I've also periodically checked Craigslist but haven't found anything yet. That having been said, I know I'm also not patient enough to wait for something to hit Craigslist.
Another option is going to a reptile expo. There you'll be able to look at the snakes, hold them, etc. You can also compare a ton of snakes! I'm going to the NARBC in August I'm hoping to bring home a snake or two for my collection.