I've gotten several grants from the county art's commission... a devision of my county government who give out small grants to encourage art in the community. I came close on a grant from a local rich guy who does artistic grants. My school had a massive school wide federal grant to internationalize our curriculum... I scored a lot from that grant. There are tons of companies that give out little grants. Target stores for example give out thousands of dollars every year from each store.
One thing that will help you a lot is to have a non-profit status booster group. It's not really hard to do, you just need a few committed parents, one of whom has a good head on their shoulders for finances as there are a few special things you need to do for the IRS. The magic thing you want is "501(c)(3)" status. But once you have that people can donate to you and get a tax deduction. They don't get one for donating to the school directly.
Next time you go to a professional or community theater
play in your area look in the program for names of companies and foundations who donate to support the theater. Contacting those people would be a great starting
point but you really need a 501(c)(3) first.