Call local businesses and ask to meet with someone. You'll be surprised how many people are willing to listen to what you have to say and support you however they can. Be prepared and professional - have a pitch ready to go for potential sponsors.
Reach out within the school community. There are undoubtedly parents who themselves are in a position to sponsor, or work for a company that can.
There are many excellent threads about fundraising here on CD, so I'd suggest you search and read the stuff that's out there. The
two stickies are not a bad place to start.
Depending on the rules of your school, don't rule out a team fee or "suggested contribution" if many families are able and willing to help.
Feel free to PM me if you need help with specific details, your business plan, etc.