CR,
The Gun Parts Corporation (GPC)formerly known as Numrich arms, will sell you a barrel of the old En Bloc clips for less than .50 cent apiece, if bought in volume. Also, there are always companies that will sell you lots of ammo that are still loaded in the clips coming from Greece of some other place out over there(Europe). My personal criteria is to always get Boxer primed and non-corrosive. Hasn't gotten me into trouble yet!