yeah what he said... you have to be providing something in return in order to get free shit... it's very possible to do, however... you have to be either what David said...or a hell of a good salesman (and then deliver in order to keep the sponsorship)
I've been in a bunch of bands who had sponsorships with music gear companies, clothing companies, etc... You just have to prove to them that it will be worth their while to be associated with your project, however possible. So really, it isn't so much "free" in the way that you are providing them payment in a different form, albeit not monetary.