Daniel's contact Dan from Florida got back with me.
He is planning to import some Natrix natrix in spring and will keep me posted.
From what I understand from Daniel - the greater the quantity of snakes imported, the lower the per-snake-price.
Here are some links to photos of the subspecies Daniel says are most readily available:
Natrix natrix scutata
http://www.dragonsroost.dk/Snoge/img/natrix-5.jpg
Natrix natrix helvetica
Stock Photo of Grass Snake (Natrix natrix helvetica) - Search Photographs Pictures Images and Clip Art Photos - D31-271513, D31-271513.jpg
Natrix natrix persa
Natrix natrix - Wikimedia Commons
There are some other Natrix natrix on that last site
Daniel says that Natrix natrix natrix requires more paperwork and suggested N.n. scutata instead, which is very similar (a little more interesting looking actually)
Rhea