Here is something I have known for a while------They may offer you contacts for what you are looking for
Welcome to the website of the Anglo-Malagasy Society, which was founded in 1961 to promote links between the United Kingdom and Madagascar.
I am putting together a multi level Malagasy Language book of the different dialects of Madagascar.  If you have any contacts or websites that show the different dialects of Madagascar, please send them my way.