In Army Men Strike, how do you obtain shovels?

Shovels (or Spade as they are actually called), can be earned free when you are lucky enough to have drawn them out as a reward in the AMS event (as they are considered rare items and a big prize). Take note too that the big prize of Spades only has 200 pieces. So technically, you'll need to be lucky enough to draw out 10 of these big prizes in order to actually avail one plot of extra building space in your HQ. Otherwise, you might want to just purchase them through IAPs