artphotodude, I recommend that you just download the APK and OBB off of the internet and sideload it. Amazon Appstore is pretty spotty (I.E. applications work with some people, don't with others) but sideloading /seems/ to be one-size-fits-all.
Note that I do not recommend nor do I endorse piracy- in this case, Dead Trigger 2 can be downloaded gratis on Google Play and Amazon Appstore, and one may still be able to participate in IAPs by sideloading- Mad Finger is not harmed.