I work for a non-profit, and we have two big fundraising campaigns every year.

First, pay attention to events that go on in your community. A lot of the time you'll see banners/marketing material that say "Thank you to our generous sponsors." Make note of those companies because they have $$$ to donate.

Second, SOLICIT. We send out letters asking for help. In the letter we include a brief blurb on our organization, our mission statement, our organization's accomplishments so far, and a brief detail of the event we're seeking funding for. If there's an event flyer, we include that too. The Children's Miracle Network is a widely known organization, so by emphasizing that, hopefully you can convince them to donate!

Ditto what the others have said about soliciting help from national HQ of large corporations. You might want to stick to something locally. Do you have a close relationship with your alum chapter? If so, ask if they have any contacts in the community and if they'd be willing to co-sign the solicitation letter. In the non-profit I work for, we have a dedicated bunch of Board of Directors from different sectors in the community, and that generates a lot of donations.

Finally, FOLLOW UP. Make that phone call. Sometimes things get lost in the mail or they overlook it. Sometimes they might have questions. The worst they can say is "no," right?