Locating grandfather's Birth Certificate

I'm hoping someone reading this message will be able to assist me.

You see I'm trying to locate whom I would have to contact if I was to locate my Grandfather's birth certificate.

Any phone numbers or email addresses would be of help.

Emmanuel Antonis CASSIMATIS was born around 4/7/1899(not too sure on his birth date)on the Island of Kithera, in a small town of Frilinginika. His parents' names were Marie and Antonis CASSIMATIS.

Hoping someone can help me with this and point me in the right direction.
Thank you
Tania