You need to go to the regional races in your area as well as some of the national level events and do well, always act as an upstanding citizen and provide information to those that are just starting out. You do all of that and if you are good enough / there is room on a team then the companies will approach you. If you feel that you are doing that and are still slipping through the cracks then you can write up a resume basically stating what races you have gone to in the past couple years and where you finished, what races you plan on going to for the remainder of the year--next season, and tell them why the company would be better off by having you as a sponsored driver...and remember you will start off at the bottom and may only get 50% off of retail to start but should have the opportunity to be re-evaluated when your sponsorship comes up for renewal.