First, Build Zombie Shield. Here’s the link on how to do that.
Second, get the Tomahawk. Here’s the link on how to get that.
Third, we need to collect 5 hidden skull. To reveal this, use your zombie shield and once you see it use your tomahawk to get the skull. Here are the locations: 1) West Ground 2) CD-Street 3) Roof 4) Docks 5) Eagle Plaza. To get the exact location, watch the video below and this can be done in any order.
Last, go to Wardens Office straight to the perk machine and you will see a table. There the free blundergat will spawn.
Note: If you already had blundergat whether its upgraded to magmagat, acidgat or its just pack. You will lose this. You can only have 1 at a time not like on BO2 Mob Of The Dead, you can have two one is upgraded and the other one is not.