Unlimited continues:
Press L(3), R(3), L(2), R(2), L, R, L(2), R(2), L(3), R(3) on the mission selection screen. A tone will confirm correct code entry.

Hint: Falling T-Rex:
At the end of the T-Rex Carnage mission, jump onto the rope above the pit wait there for approximately five minutes. The T-Rex will eventually drop from the sky into the pit.