I'm lookings for common horsetail for my bog garden.
Believe it or not, I saw some for sale recently at our local Target Superstore. In fact, they often sell plants that are suitable for aquatic use. Of course, this is here in Clearwater, Florida, but you should regulary check your local stores (Target, Home Depot and Lowes) as you never can tell when you will find bog and pond plants. You'd be surprised at what I have found and for a very reasonable price.
Uh, yeah, except Carnivorous plants sold at Lowes, Target, etc. are usually at deaths door. Plus, at least one of the companies, Botanical Wonders, admitted to me that they wild collect some of their plants. If that wasn't bad enough, they include instructions with their plants that will surely kill them, like "protect from cold" and "keep out of the sun"(presumably so you'll have to buy more).
If you are going to buy CPs, spend the extra money to get them from California Carnivores or Cooks. The plants will be well worth the extra money, and you'll be supporting reponsible good people.
Here is a link that might be useful: Cooks Carnivores