Natalie, I have ordered some from The Lily Garden she has a nice selection of lots of types of lilies.
http://thelilygarden.com/
I also got some here on ATP thru co-op's when they have one. I recently potted some up from the last one here on ATP. Just watch for one early in the year if they do another. Guess I was lucky the ones I got thru the co-op were healthy.