Becoming sponsored comes with natural progression though the game. Again, you need to earn fame points to access all the media challenges. Once you start completing the photos and videos, sponsors will offer you a chance to prove yourself by creating a video. Complete a few of these video events and the sponsor will sign your snowboarder, which will give you new clothes, boards, goggles etc. You can now take part in events and go for other sponsor based achievements.
To access your media challenges, select your desired mountain and press
to show all the media op challenges and sponsor events. You will find most of your point earnings though the media challenges, so check them on a regular basis for up to date events.