A good place to start is:
http://www.unitedcargo.com/utilities/schedules.jsp

Obviously look for 747, 767, and 777, that'll give you the flight numbers and origin and destination information.

Then you'll have to go view the availability either on ual.com (expert mode or seat maps) or KVS or ITA to check for C class availability (to tell if its 3 class equipment).