They are pretty hard to find as they are not easy to propagate. A TPT friend of mine was looking for some couple of weeks ago with very limited success.
You best bet might be aquariumplants com - they get them in stock pretty regularly, they are emmersed grown, and their quality of this plant is top notch. The plant cost and shipping cost is another matter, friend.
You might also try gordonrichards on TPT ( he is in NYC) - he stocks and can get a lot of plants.