I "know" a guy who's made it and i'm sure he'd be up to giving you a few pointers if you contacted him, he's a nice guy. His name's Andrew Wheeler and after initially aiming for the equine photography market, he found his niche in Motorsport. Here are his websites:
http://www.automotophoto.com/
http://www.whimwham.com/
of course he started out by being extremely talented, but I think rather than cold-calling, he went out there, met and made friends with the people who were his potential market, got examples of his work and put it under people's noses until they had to admit it was pretty darn good. He'll be able to tell you more. I know him from the Britnet website. He has a cool accent too
