Tickets are not easy to get during Chinese New Year, that's true. From Chongqing to Dazu, you can take bus at Chongqing Bus Station, and when coming back, you can take bus at Dazu Bus Station.
From Chongqing to Zigong, still at Chongqing Bus Station
From Zigong to Leshan, at Zigong General Bus Station
Emeishan to Chengdu, take bus at Emeishan Central Bus Station.