Hi Rock Girl!
This question should prolly go on the PE Stockroom board, where people who know about that sort of stuff are more likely to go.
Nonetheless, someone here is sure to be able to help. What major department stores do you have (in whichever city/town in Greece you live in)? Because you will probably be able to ask them to order it in for you. Also, movie rental places might be able to help you, and some music stores that also carry DVD's could be able to order you some in too. Just ring around, and see what they can do.
Sorry, but I'm not European. I'm Australian (I live in Perth) and we have had the Season 3 DVD here for a few weeks at least.
And if nobody in your town has it, maybe you can buy it from Rome, or wherever has the best shops. Perhaps you could use your parents' or friend's credit card... I once ordered "Into The Woods" (a musical) on DVD from Amazon using my parents' credit card, then paid them back (make sure you ask first!
Hope this helps. Good luck! Keep us posted!