Scenario A
Patrol 1 - Start with it
Funny-Bug - Start with it
Big-4WD - Secret car in Mission A-4 drop down the elevator shaft in the grass area to the left and behind the starting point. Must finish mission. Easiest with tank.
AUV - Complete Mission A-9
Dragon-SPL - Finish Mission A-1
Taxi - In Mission A-7 after getting off the highway near the end look for the question mark to the right in the alleyway. Get him to the last hit before you get there.
Tiger - SPL-Finish Mission A-8
Scenario B
Old-Taxi - Start with it
Super-Buggy - Start with it
Big-Truck - In Mission B-3 turn left from the start onto the road get the first Dim-Sum stand and swing around the block. Look for the ramp leading up to the second floor as you come towards the place where you got the first stand.
Tank-90 - Beat all 20 missions
Super-Car - Complete Mission A-1
Vaultsafe - On the far northern road in an indented parking lot
Yakuza-Car - Finish Mission A-9