Believe it or not, one way that seems to help find out is by looking at the driver suits (at least over the past few years anyways). The studio photography sessions that are done before the first races of the NASCAR season are the best time to find said photos (not to mention usually in HD form). As long as the driver suit itself has a camo pattern on it, it almost always matches what's on the cars.
Website-wise, search for the driver and the year they drove the car in on Getty Images website.