Once you enter Rex’s secret base, go to the lower right of the map. There you’ll find a basketball net. Make three shots to get the piece.
After the freefall, scour the next area for five red lockers. Open them for the shield piece.
In the same area as the lockers, look out for five flower pots. Smash them to get another piece.
This can only be obtained during Free Play. Use Rex Fury’s strength to destroy the strong crates. There is one in the base’s first area and two after the free fall.