Hi Beth,
I had similarly gratifying experiences when speaking to people who felt the problem. I wonder if the same people you’ve spoken to would be interested in kick-starting a clean-up group. The five of you could just go out one day and pick up litter for an hour. It might not be exactly what you want with your project, but maybe it would help you and them feel better and possibly inspire others to join or consider the way they deal with waste. And perhaps by doing a small-scale clean-up, you’ll learn some things you need/want to do/not do.
I hope you don’t mind my unsolicited advice/ideas!