Hellenic Bible Society
https://www.greekbibles.org/index.php?id_cms=4&controller=cms&id_lang=1
Hellenic Bible Society
https://hellenicbiblesociety.gr/
I do not know how good the bookstores are below.
Most Christian bookstores have some good doctrinally sound books and also carry some false doctrine books.
Ennoia Publications
Kozok Christian
https://www.xo.gr/profile/profile-910192420/en/
“o Logos” (‘Greece) Publications