You'll need to find the Security Plans in Fortnite to get your hands on another style for Brutus, either Ghost or Shadow themed. After completing 18 of Brutus' Briefing challenges, you will have the option to accept a specific mission for the alternate styles.
There are currently three different Secret Plans in the game, perhaps. More on that in a moment. They can be found at The Shark, The Yacht, and The Rig. Well, the first two can absolutely be found, the third we will discuss shortly.
Le yacht
To get the Yacht Security Plans, the easiest thing to do is go to the front corner, where it faces Steamy Stacks. Land in the water and break through the side, and you see a door you can go through. Walk down the hall and you'll come to the server that holds the security plans.
Le requin
To get The Shark blueprints, the easiest thing to do is swim through the large stone sharks mouth, climb the stairs, and go through the security door. You can just hammer it if you need. If you turn left, you will find two server rooms containing the blueprints.
The rigging
To be honest, we have no idea where the security plans are on the Rig. We've searched high and low, and even gone so far as to load into a replay and slowly noclip around the entire structure, and can't find anything. We don't seem to be alone in this either, and at this time the location of these blueprints remains a mystery. However, we're obsessed with finding them, so check back in the future if you're curious.
The good news is that you only need to get one, so the fact that rig blueprints can't be found right now isn't a major issue. After finding them, you'll need to send them to Ghost or Shadow by taking them to a mailbox, and we just have a guide showing the location of each mailbox in the game at the moment.