This is where I got my Vallisneria, Corkscrew (Vallisneria americana var. biwaensis) (10 plants per order)
http://www.aquariumplants.com/product_p/va069.htm
And they arrived looking very healthy.

Mine grew very well the first year. We had a summer drought and as the water receded and exposed new young plants I found an easy way to transplant them into deeper water. I took a long handled spade and slipped just underneath a bunch, then laid the spade in deeper water and shook it back and forth so the clump settled on bottom. There was no transplant shock and the plants kept on growing as if nothing happened. I will report this summer on how the plants are getting along.