I may be wrong for some areas, but every vehicle I know that has decals / sponsors is from somebody they have already done a lot of business with or they own that business / good friend owns that business.
Usually at best the sponsor pays entry fee / some of the money asso. with cost at the track.
I have two people that have helped me out. I've spent $1,000's with both of them and at some point they wanted to "help" with parts or labor and I put their decals on my truck. However, I still pay for most of what I get from them. Nothing is free. In return I do send both of them business.
It's nearly imopossible to get $ from a supplier / sponsor if your not already winning. If your already winning you probably don't need or want their help anyway!
Bottom line is you have to already have money to get more money!
lol, but true.