I commend your desire to start a new street press student magazine. I often pick up the free mags found at glue or general pants. Do you have a target audience, do you know much about the audience segment? What can your magainze offer your potential sponsor or advertiser?
Perhaps you want to consider preparing a business plan and post it on your blog? Or basically articulating more about your project before approach marketing/ advertising managers.
Good luck,
Berno