Unfortunately, there don't appear to be many newspaper archives on line for the time you are interested in as far as I can see. Most stop around 1945 or are more recent...at least this is true of those I've found but there are certainly others I haven't come across. However, one notable exception is "Le Monde" which you can search herehttp://www.lemonde.fr/recherche/
They may want you to pay to see complete articles. If you find anything, get back to me as my son may have a subscription (not sure if it would cover the archives though).
I would also suggest you search this site which actually sells old newspapers:http://www.journaux-collection.com/index.php
If you find anything of interest, you can again get back to me and I will try to find the paper in a library here in France - no garantee, but it's worth a try. Checking to see what came up, I put "1964" and "Cameroun" in the search engine and an article entitled "Eight assassinations in Cameroon" was in "L'Humanité", the French Communist party newspaper dated 6 January 1964.
I will PM you regarding a researcher as long as I can find out how to do it!