Part 1 - Go to the death ray and use it. Once it's used, look up and you should see a part spawned in the air. Now use the wunderspheres that's path will take you into the part. The two wunderspheres are either above Double Tap or in the left courtyard infront of the church. Use the correct wunderspheres and pick it up midair.
Part 2 - Go to the rocket pad and stand up the pack-a-punch parts. On the metal beam next to the stairs there will be a switch that should have a red light. You can flip that switch once the rocket starts doing its test fire. Make sure to flip it and immediately run to the doors where the teleporter is, or else you'll go down. Once the test is over, go next to the teleporter and interact with the panel and the part will spawn in the teleporter.
Part 3 - This can be obtained by killing a panzer which spawns on round 12. The part will spawn directly above the panzer's body.
Craft - You can craft this at either the table in the wall next to the pyramid in the undercroft, in the room above double tap, or in the back of the church next to the dragon head