In such a case some familiarity with Greek is called for.
First of all, you haven’t given much so far about the actual briefing of the commission; context: what for and how? a book title? a restaurant signage …? Is it to design a brand or to provide text for repeated use, based on encoding? Which media involved? Target audience??
And “5th c.y Athenian” has damn nothing to do with esoteric, where did you get that from? If that task seems “esoteric” to you, you’d better hand it over to someone else.
If you still want to do it on your own (?!) start with the 1st step first and look into Greek script history. Then study relevant encodings and search for fonts …