Acquire Steel Wheels Car:
Input the following password at the cheats menu: U84D 3Y8K FY8Y 58N6

Acquire More Paint:
Acquire the Elite level license, then you can use gold paint. Acquire 100% completion file attached to your Elite level license, then you can use platinum paint.

Get Cars:
Get Carbon Hydros Custom - Finish all Showtime Road Rules.
Get Carbon Ikusa GT - Finish all Time Road Rules.
Get Rossolini Tempesta - Acquire an A Class License.
Get Carson Fastback - Acquire a B Class License.
Get Nakamura SI-7 - Acquire a C Class License.
Get Hunter Mesquite - Acquire a D Class License.
Get Carson GT Concept - Acquire a Burnout Driving License.
Get Jansen Carbon X12 - Land All 50 Superjumps.
Get Montgomery Carbon Hawker - Break All 120 Billboards.
Get Carson Carbon GT Concept - Break All 400 Smashes (yellow fences).
Get Krieger Carbon Uberschall 8 - Complete 2 Sets of Online Challenges.