Sorrry, I did not guess that AOC is exactly as COA in italian: Certificato di Operatore Aereo.
I could not find it in the ENAC website, It must be there but I should spend more time in searching it.
Since Italy is a member of JAA and is implementing JAR-OPS 3 I searched and found something here:
http://www.jaa.nl/publications/jars/606970.pdf
Go straight to page 145 of pdf document. I did not investigate about classes of single engine helicopters. Most of time in Italy will be an AS350.
I will go deeper in this matter when I have some quiet time. This is interesting, if you investigate before me, let me know.