Is there a bus between HKIA or anywhere in Hong Kong to Guangzhou airport,

I'm afraid no direct bus is available for the trip(s). To travel between HKIA, you can take a direct cross-border coach to Guangzhou first. Then take a local taxi to Guangzhou Airport! If you will depart from HK downtown, you are recommended to take a train at Hung Hom Railway Station to Guangzhou East and then transfer to local subway line 3 to the airport!