To get the "good" guns you need gold. To get gold, you have to spend money. There is a button for "Free Gold" I assume you have to watch commercials of other games to get the gold(thats how it works on other games) but when you click on the link it conveniently says "Connection Unavailable. Check Network" but if you click on a link to purchase gold, it works every time.
Alaskangirl907 about Contract Killer: Zombies, v3.1.1