Hello Tanya,
You could try checking your national government department for more information on what documents you might need for getting married overseas/abroad in Guinea (the government department that deals with all matters regarding births, deaths and marriages (including overseas ones) etc. Also is there a Guinean embassy in your home country? if there is none, you could try visiting the nearest embassy to your hometown or home country for more information about document requirements, including affadavits. Best wishes :-)