I don't mean to be rude, but you need to show why you deserve help instead of begging for it. As a 20 year old in B class, wanting to get your pro license, what do you have that tons of other kids don't? Start with some organization and professionalism... write down your thoughts, and schedule. Proof read. Change it. Come up with a good schedule of events that you want to do next year, along with previous results. Throw in a detailed objective. Specify how you will promote your sponsors, and get their name out there. Contact someone to help you make a good resume - if you are giving your resume to an outside industry company (construction companies, tattoo shops, car shops, any local businesses), which is the best bet for cash donations, add a page showing your bike and transportation that shows the area where your sponsors graphics and name can go to advertise... outside industry sponsors sometimes dont have clue whats going on (use a picture from decal works of a bike that says "your name here...etc)... You seem like you have the desire to do something with it, but you have to realize how slim the chances are. If you really want to take a shot at it, and need help, then you need to put yourself in the position where people WANT to help you. Also, for local businesses, go in person! Do not just send a resume through email, or mail... Either walk in, or call first to schedule an appointment. Let these companies know that you will tag them in photo's, results, and season updates on facebook (if your facebook is appropriate, which it should be with a goal like this) for additional exposure. Think outside the box.
If you want to do it, then put yourself in the position where you can do it... but youre going to need to work just as hard off the track as you do on it and in the gym.