Hah.. , at last. I know this one!
As far as Greece is concerned, you can try to get certified in Chalkidiki, which is close to Thessaloniki and not very far away from the borders. There are a lot of Thessaloniki - based diving schools there. I can strongly recommend Sea World - well, that is my school so I like them-
http://www.seaworld.gr. Sea World has a gives diving classes at the Sunny Hotel at the first Peninsula of Chalkidiki, which is also a great place for summer holidays. The sea there is really calm, and diving is very easy for a beginner. We never had pool sessions, since the sea was exactly like a pool. We had approximately 8 theoretical classes and 6 dives before we got certified. I think with a full schedule the teaching period for the first star C.M.A.S. will take you approximately a week.
There is aslo Triton (
http://www.tritonscuba.gr ) which is also Thessaloniki - based and gives classes to the first peninsula of Chalkidiki. I have never dived with them but I have dived to the location they are based. It is a beautiful place and I have to admit that diving there is more interesting that the diving sites at Sunny Hotel. Still, it is more "difficult" so I do not think it is ideal for learning.
There are a some more diving centers in Thessaloniki and Chalkidiki but I do not know details. If you decide that Chalkidiki will be your destination I will be glad to make a recearch for you. In any case, Chalkidiki is a great place for summer holidays and you can combine holidays with diving classes. I am afraid that you have to wait until next year though. The weather is getting kind of chilly and coming in Chalkidiki in the winter is not that fun. If you do not want to wait, you have to really hurry. September is the last - and probably the best as far as prices are corserned- month of the summer season.
Well, whatever you decide, have fun and take care!