[nbetik]

In my limited experience, having a contact of some kind is one of the most useful things to have. Sometimes individual employees will have "sponsorship budgets" which basically means they have X amount of money per year to give to charitable/community organizations (although I would be careful with this, i.e. it would be good if you know the person very well). Also, get in touch with existing sponsors, because they may be willing to refer you to other companies/corporations they do business with.

Good luck!