Sir,
Actually, a few coaches of this train are detached at Moradabad. The detached coaches form a new train (called slip train) and go on to Ramnagar. The rest of the train goes to Kathgodam(original route). The detached coaches which goes to Ramnagar only have 3AC and Sleeper class.
This is the reason that u r not able to book for 2AC. Please try to book in 3AC. This is a daily train. So no worries about date.