Birth or baptismal records

Who or where would I be able to obtain a copy of my fathers birth certificate or baptismal certificate--OR any document that would serve as proof of being born on Kythera (Fratsia)?

I am informed that births prior to 1900 are very difficult to find.  I genuinely THANK YOU for any assistance or advice.

I may be reached at: yiayiabeck@hotmail.com