I think for the sake of having any Green cards in the set, I'm going to have to say the Japanese traditionalists - the Japan Liberation Front and similar - are green. They're rebels and freedom fighters like the Black Knights Faction, but motivated more by "maintaining traditions and remembering the past", and they're more stoic/accepting/spiritual than other rebel forces.

I'm actually considering bringing back Bushido as the keyword mechanic for the Japan Liberation Front :) It has a great association with Japanese tradition, plays well, and interacts fairly well with power-boosting mecha.

In particular I think the Four Holy Swords are very green in their philosophy, even as they fight in mecha to defend their homeland and eventually join the Black Knights.