Start with whatever list your high school has complied. Watch the local paper for congratulatory announcements, keep track of those organizations. Check with your credit union, employer, etc. The Elks were very generous to our D, so check with Elks, Lions, Women's Clubs etc.
If your kids have have earned the Girl Scout Gold Award or Boy Scout Eagle, search for those (Gold Award Scholarships). If they have a hobby, try that. It can take some searching.
You can try fastweb.com, but I'd use a separate email address (just set up a free one you can check from time to time).
Good luck.