Look in your yellow pages for a pond builder or an irrigation equipment dealer. Alternatively you could call local nurseries and ask who carries water plants.
Lily pads or water lilies are my favorite plants. It used to be that you had to go to specialized water gardening shops. But, now you can find them at large garden centers, including some that are connected to hardware stores.
You can buy them at any local green house and I know walmart sells them as well the only hting is that if you buy at walmart you may be limited as to what colors you are able to chose from.
you should go to a garden store in your area they will sell everything you need for plants. if that doesn't work try going online to a garden store and buy them that ways