GTA SA secret vehicles location

After 2 weeks of hiatus... Here I go!!
 
Girlfriend's cars
Obtainable after you date her to %50
Green Hustler - Date Denise to %50
Bandito - Date Helena (Her car doesn't have any doors)
White Romero - Date Katie to %50
Monster Truck - Date Michelle to %50
Police Ranger - Date Barbara to %50
Pink Club - Date Millie to %50

Winnable cars
BF injection: Get first place at the dirt ring race at las venturas stadium. Also rarely spawns at SF outskirts.
Bloodring Banger: Get your total time up to 1 minute in the Bloodring
Bullet: Get all silver awards in driving school. Rarely spawns at Vinewood Hills.
Dune: Beat the score of 25 at the Dirt Ring
FCR-900: Get all silver awards in bike school . Also common spawn at all cities.
Freeway: Get all bronze awards in bike school . Also common spawn at LS countrysides.
HotKnife: Get all gold awards in driving school
Hotring Racer: Get first place in 8 - Track.
Hunter: Get all gold awards in pilot school to spawn one at Verdant Meadows Airstrip
Hydra: Beat the mission, "Vertical Bird" and it will spawn at your airstrip
Jet Pack: Complete the airstrip asset near Las Venturas
JetMax: Get all gold awards in boat school
Marquis: Get all bronze awards in boat school
Monster Car: Win it by beating 8-track
NRG-500: Get all gold awards at Bike School
Rustler: Get all bronze awards in pilot school
Squallo: Get all silver awards in boat school
Stunt Plane: Get all silver awards in pilot school
Super GT: Get all bronze awards in driving school