It'd be pretty easy to make some basic software to do it I'd imagine, using MS Access. Store data for all the referees in one table and their availability in another. You could create forms for entering new referees, appointing referees and stuff. All it's doing essentially is putting a bit of decoration over what is essentially an Excel spreadsheet.
If you're handy with Excel then you shouldn't have much problem storing your referees data on it along with their availability and using the filter to only show referees available on a specific data.