Best advice - just give up! Trying to get any information out of Zimbabwe is like pulling hens' teeth. Deaths, up to c. 1977, are available through Family Search but nothing else. All that being said, if you know when he was born and know someone in Zimbabwe who could go to the relevant office you might be able to get something. Or you could write to the Central Register Office in Harare - but don't hold your breath. Be a bit careful about people offering to do research - they are so desperate for currency they will promise the earth but produce little. If you do get a certificate hang on to it - trying to get a replacement is near hopeless. Sorry to be such a Job's comforter but it is from personal experience.