Getting sponsors means a serious commitment to the business side of fishing. You will never get anything (even a 10% discount) for nothing. You must be willing to do more than slap a decal on your truck! You will be working shows and other events...and I mean working!
Start small...decide what your goals in fishing are...develop a 1 yr, 3 yr and 5 yr plan on where you want to be and how you want to get there. (Believe it or not, I reached my 5 yr goals in 3 BUT turning full time pro is a ball buster. I work 18 straight days at the Houston Boat Show for example...and you can't guide then so no money coming it!)
Once you have a plan, go after the sponsors. It is all about what you can do for them NOT what they can do for you...don't ever forget that. Ask for nothing at the start and see what is offerred. Usually it will be some form of a discount. If you are looking for free product. go to the shows and take the free stuff thee because sponsor don't do that at first, if at all. I have been very lucky (or good a promoting) as all my non-boat related sponsors give me the product I NEED---not what you want and not what you would ever give away. That is one of the quickest ways to get canned. My boat deal is a sweet deal, and I mean sweet, but it is not free and it is not "dirt cheap." I got my boat deal YEARS after dealing with my dealer. I had already purchased TWO boats from him and had helped him for years hauling boats to and from the shows and working the shows before I even dared to ask about a pro-staff deal.
Remember, walk before you run. Also remember this is a VERY small business community. Many (most?) of the people you deal with at these companies jump ship and go to others quite often...NEVER, EVER, burn a bridge by ticking anyone off! It gets around, whether true or not, it will kill you future.
Hope this helps. If you ever get to Clarks Hill we can talk some more over lunch or something.