What you have to do is put together a resume and send it to the company. Check www.ncbf.com and search for that topic on the message board. It's been asked a couple times there, along with what you should include in a resume. For bass fishing, it's stuff like tournament statistics, charity tournaments you've participated in, etc. Salwater is way tougher, that's why there's so few guys with saltwater sponsorships. Remember, companies are looking for somebody that can sell their product, not just somebody they want to give free stuff to.
-Brian