Start at the Guangzhou East Railway station. You can take the Bus 280 and get off at Guihuagang Stop, there take the dark green bus (Fudu Bus 富都大巴)， it will take you directly to Shiling Leather Town.

For the trip from Hong Kong Airport to Guangzhou, there are buses between these two places. The departure time:
07:45 08:05
08:50 10:45 12:45 13:45 14:45 15:45 16:45 17:45 18:45 19:45 20:45 22:45

There is a shuttle bus from The BaiYun Leather market to Shiling every 20mins. from 6:30am to 7:00pm, and you only have to catch 1 bus. Drops you off on the main street of Shiling and you can see the markets from the bus. Bus can take approx 1 to 1/4 hours.

Or you can take a taxi from Guangzhou to Shiling, for about 150 RMB and takes approx 45 minutes. However, you will need to get a bus back as there are no taxis in Shiling.