Serpent offers a wide range of optionals parts for the offroad cars.
Its easy to find the full list, by selecting the car of your choice, and then select optionals from the car-menu.
Direct links:
S811 Buggy http://serpent.com/product/600001/optionals/
S811 Truggy http://serpent.com/product/600030/optionals/
For Truggy more optionals in the process already.
Team Serpent