Go to the Wichita Gardens area and drive around the buildings until you see an Angel motorcycle abandoned on the side of a building. Get on it to begin the AWOL Angel high-score side mission. This mission rewards you with rockets when the mission ends, either by killing the driver or destroying the Angel. You will receive a decent amount of rockets that will end up at the 9999 maximum after five to eight mission sessions. Note: No new high score is required to receive the rockets.