I have had one person on a Freecycle sit that gave some plants but that is the only one I've found. Totally agree with the comment about price of pond plants.
I always think of water lilies as being a bit like Acers. Sycamores are cheap as chips and the same goes for big lilies - plants such as N. alba soon make a rootstock you can hollow out and live in, whereas pygmies like N. helvola spend a lot of time on nurseries growing up to a saleable size. So many people buy cheaper lilies and end up having to give them away or hack them up when they outgrow their pond. The same thing happens with ghost koi..
I'm even tighter still - much of my wildlife pond stock comes from cuttings collected locally.
I've bought a couple of lillies off ebay, not that good...they put up a couple of new stems last year and this year nothing and definately not any flowers