There is no direct bus from Guangzhou Baiyun Airport to Macau, but you can take a bus at airport to Zhuhai Gongbei , when you arrive at Zhuhai Gongbei Coach station , walking to the Gongbei Port about 10-15 minutes.
If you want to experience the High Speed Train in China, you may take a high speed train from Guangzhou South Railway Station to Zhuhai Gonbei. The train will stop at Mingzhu station and at Zhuhai also. You need to take Metro Line 3 at the Airport, transfer to Line 2 at Jiahewanggang Station. The last stop will be at Guangzhou South Railway Station. The first High Speed Train from Guangzhou South Railway Station to Zhuhai is at 06:60am, the last train at 22:45pm; travel time is about 60 minutes and costs 70 Yuan. ( How to Get to Guangzhou South Railway Station from Guangzhou Baiyun Airport )
It is about 5 minutes walking from Zhuhai Staion to Gongbei Port, after clearing custom; you can take the free shuttle buses of different hotels at Gongbei Port to Macau.