I work at a restaurant. We have probably about 20 requests a week for donations. So you're not the only one. We try to give a gift card to everybody. But some people want more than gift cards, i.e. food, paper goods, etc. It's really difficult to give to everybody, since we're struggling in this economy big time.
All you can do is go door to door and ask nicely. You will get turned down a lot. I used to do this when my older daughter was in high school softball, and it wasn't my favorite thing to do. Don't take it personally. Also, make sure you ask all the parents if they have any connections or if any of them own their own businesses. Maybe they can help out.