winning and making them money. No company will sponsor you unless they get something out of it. I know a bunch of sponsored guys but how did they get them? by knowing many people in the industry and doing promo work for the company.
You approach a company and lay out how you can benefit them. Supplement companies want someone who can say "take this from X, and you'll look like this, or your be able to do this..."
I myself am not sponsored, but I promote my team (Team Barbarian) here in Toronto all the time. I do it for free, because I train with them and work with them. I do it to further my friend's businesses. They are working to make a name for themselves by proving they can train the best.
With that said, I know top competitors in Canada who aren't sponsored either.