Actually it's a brilliant marketing strategy. The plan from the beginning was to release it with the Vengeance map pack correct? They could have just waited until the 2nd, or even just release it early for season pass holders but they they were nice enough to make it attainable for EVERYONE. With that said, it's still meant to be a dlc gun so there not going to let you get it within your first 5 box hits. I feel it makes sense to make it hard to get as it wasn't meant to be on the maps for everyone unless they plan on buying the dlc. Yes it might be pretty time consuming but the gun is definitely worth it and players will eventually experience this which may sway a lot of players into buying the dlc that wasn't planning on it before.
If you've been having trouble getting it I advise you to just stay in the same game until you finally get it because if you keep starting up new games then it's just going to take that much longer.