who is and were and contacts of an authorized Chinese government office

i am a Nigerian residence in Ghana, a Pastor and also a Business man. i learn that to get a Chinese entry Visa to China after your invitation. you need a confirmation of invitation letter issued by an authorized Chinese government office, which is also very much required. were do i contact this People as in authorize Chinese government office. or does my invitee get that in attachment to my invitation were is the contact of this authorize government office?