Our association has been using iSOCS, Internet Sports Officials Calendar and Scheduling System. It does not support the features asked for in the original post. We have used it 5 years for basketball, I have been the assignor for the last 2 1/2 years. Charge is $0.33 per game. I could not assign without it. It supports multiple sports and claims to have over 4000 customers.
http://www.isocs.com/default.asp