I believe the one Rilo refers to maybe in the little church up in Avliotes run by the nuns, Corrina being the head nun there, this being Ayia Paraskevi chapel. They have hundreds of plastic chairs and tables and a live band, stalls selling candy floss, toys for the kiddies, and then long trestle tables with bbq's behind selling fresh kebab sticks served with bread and lamb on the spit, beers and wine by the jug. You grab and table queue for your lamb and kebabs and as then night goes on the band plays all the traditional folk dances which everyone is invited to join in. Its all very rustic and full of village atmosphere. My favoutite one of all the Panayrias (local festival).
Actually during the months of July and August there are village festivals all around the islands villages and the dates are normally posted on banners around the road sides inviting everyone along.
The biggest name day being August 15th for Maria. A national Holiday in Greece.
San Stefanos also had one last year held in the area across from Athens Bar up the little lane there.
In Arillas they have the wine festival as well a little later normally in September.