How do i get source files or source codes?

[NaN]

Do you need the acceleration values explicitly or are current position, orientation enough?

Code:

// graphics interface, interpolated!
void Update(); // update interpolated chassis state
const MATHVECTOR <T, 3> & GetCenterOfMassPosition() const;
const MATHVECTOR <T, 3> & GetPosition() const;
const QUATERNION <T> & GetOrientation() const;

If you want to use the non-interpolated values I would suggest to derive from cardynamics and read the btRigidBody values directly.