It's very common--you should be able to walk into any Home Depot, Lowe's, etc and find it in the houseplant section. If you get it at a place like that it won't be very expensive either. You might have a hard time just finding one stalk though, typically you'll find a few stalks together (still not expensive though)
I know that our petsmart sells it in the fish /aquarium dept . That is where i bought my last one and both of them are doing very good . make sure while growing them that you change the water often and also use water that has set out more than 24 hrs in a jug i use the huge hawaiian punch jugs and also milk jugs and I water all my plants with the water that sits out more than 24 hours . I hope i have helped . take care .