There are unlikely to be any more additions to the OOB set.
The flag page is full up - Georgia uses a space for someone who was there earlier, I think, but not there post USSR.
The only other way would be to make all the flag button pages have 2 pages and a swap page button, which is clunky and would entail a heck of a lot of code.
And frankly - any additional orbats would be for minor nations and
each one would bring a horde of extra OOB research and maintenance, that
isn't really worth the bother. Red and Green (and possibly UN - probably the
least used one
!)are there for scenarios or mods for unavailable minors.