Instructions
Complete the "1A" license with at least a bronze rating. You will be awarded the Dodge Ram pickup for this and can enter the pickup race.
Go into the used car dealership in-between races. Every time that you enter a race, six new cars spawn automatically in the dealership and the oldest ones disappear. Check the stock to see if a pickup has spawned in the dealership. Skip the truck race until a pickup spawns.
Speed up the spawn process in the dealership. Go to a race. Go to the start "Select" screen with the checkered flag to start the race. Click on "Exit." Do this five times. Go into the used car dealership to see a larger selection.