The Problem is that the Romulan Republic is not a strong Galactic power, is a weak one, its made only by refugees, exiled and renegades colonists from the former empire. They have a common goal, live in peace but not affraid in use weapons.
Being a poor and small galactic power, means that they don't have the resources and personel to build starbases and more ships.
so no green Starbases and Fleet Warbirds, Unless, of course, that the FED/KDF are willing to design and build Fleet Romulan Ships (Story/Lore Wise). the only way that the romulans can have Fleet Warbirds from allied starbases is Romulan Addon/Project/Shipyard for each starbases(Gameplay Wise).