Is there still a direct bus from Xinnanmen to the Chengdu panda research base?

I just searched for that and none of them operate for this route any more. The panda base is only around 10 miles from Xinnanmen, so you can take a taxi to reach. The taxi fare is CNY30-40.

You can also take a city bus to the Panda Research Base. For example, Buses 34 and 27 go clockwise and counter-clockwise around the First Ring Road, and both start and end at the North Railway Station. Worst case, take a taxi or the subway to North Railway (second to the last stop on the #1 line) and you can walk to the bus station on the West side of the train station, transfer to the #9 bus to the zoo stop and from the zoo stop bus #87 goes directly to and from the Panda base. Your 2 yuan bus fare will be good for a couple of hours, and the trip takes less than that, so you can make the trip for 2 quai if you can figure out how to get to the North Rail Station and get on #9 to #87.