www.coursera.org has courses on Sustainability taught by university professors. You don't get college credit, but if you want to pay a small fee, you can get a certificate that recognizes you finished the course. The fee is about $50 US, but they have financial assistance.
Choose Courses from the menu and search on Sustainability. Be sure and look at the bottom of the page for other related classes. Also, consider taking courses on the World Economy and how the logistics of the business world works on an international level. It will give you insights as to what motivates business decisions that are made on a large scale. Remember, if sustainability cannot be done profitably, it can't be a part of commerce for long. That's the nature of the world economy. It's not bad, but people have to eat.
Check it out