Well I'm sure the EB team will work something out that's presentable. They always do.

My best bet would be something like

Roman
Greek
Celt
Nomad
Phoenician
Iberian
German

Lets see... In no particular order

Romani - Roman
Epeiros - Greek
Koinon Hellenon - Greek
Makedonia - Greek
AS - Greek
Ptolemaioi - Greek
Karthadastim - Phoenician
Lusotannan - Iberian
Aedui - Celt
Casse - Celt
Arverni - Celt
Sweboz - German
Getai - Celt?
Pavlah - Greek/Nomad (depending on govt, I suppose)
Sauromatae - Nomad
Saka - Nomad
Saba - ?
Backtria - Greek
Pontos - Greek? Nomad? What?
Hayasdan - Nomad?


Of course there are cultures that are only used once that could be replaced with something else. German and Celt culture are close enough that they can share, and Iberian's are as well. I can also see a case for Persian or Armenian (Persian could be more inclusive than Armenian, perhaps). I don't know anything about the Saba other than glancing at it's info while choosing a campaign.