Here are the locations of Black Market Vehicles.

Makoto MZ 250 (Black Motorcycle) - X20401 Y24964 / Sungal Tapal
Pell Silverbolt 6 (black Aircraft) - X9454 Y5760 / Teluk Permata Airport
MTA Powerrun 77 (black speed boat) - X20656 Y31047 / The island southeast of Pekan Kesum
Garret Traver-Z (black sport car) - X6415 Y24454 / A crossroad with no mark, the car is parked near a fence
Rowlinson K22 (Black chopper) - X15884 Y4287 / Bandar Baru Nipah (On the roof of the smaller building around the skyscraper with the telecom array)