In [48 Hours][1] they destroy the last functioning DHD on earth in order to save Teal'c, however at the same time they establish at least a rudimentary knowledge about how to hook up and unhook a DHD device. It has also been proven in many other times that they can dial the gate without the DHD.

What stopped them from going to some uninhabited back water world, unhooking the DHD there and bringing it to earth so that they could have a fully functional DHD?


  [1]: http://stargate.wikia.com/wiki/48_Hours