You can only find this free battlestar after unlocking the That's a Wrap Loading Screen.
This is the That's a Wrap! Loading Screen for reference:
Notice the battlestar on top of the food truck.
The spot is found at the SW part of Greasy Grove, on a red "Fork Knife" food truck. Climb onto the Food Truck and collect the Battlestar.
See screenshots and maps below to help find the location of the secret battlestar.
- You can only locate the Week 6 star after you have unlocked the That's a Wrap! Load Screen.