Check locally. We are far from upper class, but we live in a low SES region so we are much better off than most. We have a couple of large trusts that either give $$$ to a large number of kids or handle dozens of local scholarships. Outside of those, check local branches of veterans’ groups, credit unions, and places like the Wednesday club. Grades are important, but many also focus on leadership and community service.
Our school’s guidance office puts out a newsletter that contains many of them with deadlines, etc. so you may want to start there first.