If you haven't already, pick up Season 4 right now. If sales don't pick up than we will not be getting Seasons 5 & 6 on DVD. It is not available in stores but you can buy it online.
Purchase from Shout directly: http://www.shoutfactorystore.com/prod.aspx?pfid=5257099
Purchase from Shout's official seller on Amazon: http://www.amazon.com/gp/offer-listing/1603993428/ref=dp_olp_new?ie=UTF8&qid=1278475350&sr=8-3&condition=new
If you don't have a credit card, purchase a Visa gift card at a store and use that to make your purchase.