+30 210 3534315 Try calling them on this number. I was in Athens three days ago and the email worked. Im back there in a couple of days, I'll check their email address and let you know.
This is outdated, but may be of help;
AOPA Hellas Flying in Greece
Lastly, I would try and contact Kyprianos Biris of AOPA Greece. They have negotiated good rates for small GA aircraft.
[email protected]