Dauben's the smallest waterlily I've grown, and it's available everywhere, including my favorite aquatics provider, texaswaterlilies.com. I know there are other miniatures available, but I don't have any experience with them. I'll ask around with my nursery sources. Hopefully someone else here has some ideas.
Now, if you happen to have a N. thermarum or something, we may need to have a talk...