When we went a few years ago, the earlier trip was sold out and we immediately were sold tix for the next Haunted Hayride. Perfect! We popped into Trail's End Buffet, had a great dinner, toured around FW - we'd never been - and got on our ride.
I think the tickets were not for sale in advance - it was a "day of event" type thing. That may or may not have changed.
But SHHHH! So many people don't know about it! It was one of the most awesome experiences we've had in all our WDW trips!!!
melomouse