I dont think you will find rental Alfas here, plenty of Fiats though. Same thing nowadays
Some web addresses: avis.gr, hertz.gr, budget.gr, antenarac.gr. The last one belongs to a group selling alfas (in addition to vws and audis).
Enjoy your stay and keep some water tanks with you at all times to help us put out forest fires. And if you find yourself in the vicinity of one, DONT DONT repeat DO NOT listen to the guys in uniform.