There are many online stores and nurseries to buy from. You can also find some for sale at places like Home Depot, Lowes, etc but they are mostly sick due to the store's inexperience with growing them.

Here are some places to buy from:
http://www.californiacarnivores.com/
http://www.bugbitingplants.com/
http://www.growcarnivorousplants.com/
http://www.flytraps.com/Scripts/default.asp