I was in Greece in 1971, I saw plenty of guns there under the military dictatorship of Papadopoulos, and a very worried populous.
Weapons were surrendered by the Greek guerrillas after the
first round of the Greek Civil War, pursuant to the Varkiza truce of Feb. 19, 1945:
Coincidentally, this was right after the Yalta Conference, where Stalin conceded to the British a 90% sphere of influence in Greece. Orders went out from Moscow for the Greek Communists to disarm, and most of them (reluctantly) complied. But you can see from the picture above that the surrendered weapons were not the best in their arsenal.
There were holdout groups, and the guerrilla movement was reconstituted in 1946, leading to the second round of the Greek Civil War, which lasted until 1949. At the end of that, there was no mass surrender of weapons. They just went underground.
There was another huge influx of weapons (mainly AK-47's) after the fall of communism in neighboring Albania, in 1991. So between the WW2 holdovers, and the Albanian AK's, Greece is awash with illegal guns. People just ignore the laws when it suits them.
There is sort of an unwritten understanding in Greece: the authorities won't push gun confiscation too hard, and in return the dissidents won't use firearms in their (many) riots and demonstrations. They content themselves with liberal use of Molotov cocktails. (And incidentally, the formal Communist Party (the KKE) is highly disciplined. They demonstrate, but never riot. The troublemakers are various Maoist and Trotskyite offshoots, and just plain nihilists.)