Put your number up at other stores. Or just call around and see who needs coverage. People are leaving town left and right or want to spend time with their family right now.

Are you in a licensed store? I've never heard of contracted hours on the corporate side in the states. I don't mean to be harsh, but unfortunately this sounds like a lesson in negotiating your contract at your next position. If you're only contracted for eight hours then I don't know if there's much else you can do. Maybe if you're in a grocery store you could ask to be cross trained in other departments to pick up hours? Or if your parent company allows it try to pick up hours at other locations? You could also try posting a memo near the schedule for your coworkers to reach out if they have shifts to give up.