Kindly refer to the following websites:

The Immigration Department of the Government of the Hong Kong Special Administrative Region: 

http://www.immd.gov.hk

Public Security Police Force of the Government of Macao Special Administrative Region：http://www.fsm.gov.mo/psp/eng/main.html

If you want to apply for a Hong Kong tourist visa,you can also apply at the Chinese Visa Application Service Center in Phnom Penh.