Contact them.
Ask them if their interested, and you will run thier sticker or use your car for their booth at a show.
Also get to know the people in the show's, like other nice cars....my buddy got fully sponsored by HKS!! for is gold RSX...but he is heavily involved in the scene.
be aware of contracts they might want you to sign.
btw, can you post pics of the car that want to be sponsored?