Unfortunately, none of the existing fixed load outs have this as a kill streak so you have to buy it in a custom load out, and then equip it.
The other negative is that it is very expensive at $50,000, so it will be later in the game that you have funds to unlock it.
When you have the funds, purchase it and equip it. Then play (only a suggestion), free for all with bots on a map like pier 70/seascape. These are small maps, and you can rack up a lot of kills, and as such, will likely be able to deploy this within 1-2 games.
Good luck!