How to get a Hong Kong Visa for my Son in Colombo?

Dear Sir,

I am a Sri Lankan citizen and travelling to Hong Kong and PR of China Frequently on Business with my wife. We both are holding Multiple Entry Visa to both these Countries for the past three years. We intent to take our son, who is student, for the FIRST TIME with us to Hong Kong. When I approached the Chinese Embassy here in Colombo with his Visa application together with the Invitation Latter from my Sponsor, travel itinerary, hotel booking, sponsor application and all other relevant documents to obtain his visa in One Day., I was told that I have to apply in Hong Kong to get his Visa. I will be very much thankful to you if you could kindly help me to get his visa in Colombo as I have to travel to Hong Kong on or before the 21st 0f Sept. for the inspection of the for which I have already placed orders. Please reply me asap.

Regards
Mowlana