The website of the General Archives of Greece has a specific area where digital images are being uploaded: http://arxeiomnimon.gak.gr/index.html. This site is not easy to navigate, but with patience and the help of an English translation button on the right side of the website, it can be done.
A pdf file with step-by-step directions can be accessed here.
As can be expected, most of the files are in Greek script. However, there is a valuable collection of Electoral Rolls from the late 1800’s which has been typewritten in Greek — and the names are easy to read. This collection contains lists of men who were eligible to vote. It is sorted by Nomos (County), then Districts and Municipalities. Instructions for accessing this collection titled “Election Materials from the Vlachogiannis Collection” is found at the end of the document. A direct link to this collection is: http://arxeiomnimon.gak.gr/browse/index.html?cid=586603
A sample page of the Election Rolls is below. The Nomos is Lakonia, the village is Agios Ioannis (Sparta). The columns are: 1: line number, 2: first and last name of the voter, 3: voter’s birth year, 4: name of voter’s father, 5: voter’s occupation.
My great-grandfather, Panagiotis Papagiannakos, is on line 1975.