Start with
http://www.victoria-adventure....
That site hasn't been updated, really, in around five years, so the sources given there may or may not be useful. Seeds are hard to come by from resellers because they have to be kept in particular conditions (i.e. wet and between a certain temperature range) and because success rates are so low, especially for beginners. Survival of shipped plants can be hit and miss. I'm told that you're in the right part of the country to make it grow, though. If after reading the material at the above site you still want to give it a go, I can probably dig you up some direct sources to try.
A much easier to grow alternative for monster water lilies is Euryale Ferox,
http://garden.org/thread/go/16..., also mentioned on that site, but very spiky and without the stately upturned edges.
