I don't. But, I've always wanted to go. We used to have a Greek pipemaker on the forum. He might have had some information that would have helped you. Maybe one of the other Greek members will chime in.
There are 2 or 3 good pipe shops in the centre of Athens nearby Panepistimio metro station (the Rentzi Tobacco House and also the Cassano tobacco shop Athens)...for pipe tobacco is not worth trying searching, there are only few brands and overpriced (e.g. Amphora full 10euros, Davidoff scottish 18euros, Captain Black 15euros, Skandinavik 11euros e.t.c)
'Never been. People love Greece and don't want to come home. One caution, in some of the seaside villages, islands and otherwise, some of the old stone stairways to the shore have eroded away and drop off mid-stairway, and aren't marked. A friend had plenty of wine and almost walked off into eternity. But as long as you watch your footing, it's pretty wonderful, I hear.
I agree with liber76 the choice of tobacco here is not good,Amphora,Borkam Riff,Scandinavic,Captain Black and Davidoff are your choices.
There is a Greek producer Wolfway Tobacco,they have a place near Syntagma Square.
Wolfway Tobacco point, Βουλής, Στοά Μπολάνη 7, Athina 105 63
They do a line of pipe tobaccos under the Medusa label
The Greek pipe maker mentioned is Michail Kyriazanos who is on Paros Island,I have a couple of his pipes,he is doing some lovely work.