I don't buy my stuff online.
I have gotten the DVDs that I have from Borders, Barnes & Noble (book stores in the states), Circuit City and Best Buy.
I also get stuff from a place that specializes in used CDs and DVDs.
You might try e-bay if you don't mind it being used.
The above places have websites that'll come up if you do a Google search.
I know Barnes & Noble is www.BN.com