You might need to double check that those SD packs are actually available to buy. They are on the site; I tried to purchase some and was told that they are not available any more. Admittedly I was told this a few months ago, so things may have changed, but just check before you commit to purchasing online.
As for making your own SDs, that can be quite easy. The Shield Generators from Crisis suits can be glued onto the underside of the Gun Drone instead of the Pulse Carbines, or you can just drill a hole in the bottm of them and stick them onto a flying stand. Cheap as chips!
E.