If you look in the game folder under resources/entities/campaigns there are a few files called philip.xml, sandbox.xml, etc. If you open these up in a text editor, all of the factions in that campaign will be listed near the beginning in a format something like this:
<faction enttype='Argolis'>
<baseincome>1000</baseincome>
<maxfactionid>51</maxfactionid>
</faction>
with that being the definition for the Argolis faction. To add a hoplite brigade for the argolis faction you'd type:
addbrigade hoplitebrigade -faction Argolis
You will find that some of the names in the file match what you see on screen while others are a little different. For example the Odressyian factions are just called ThraceEast, ThraceWest, etc. There are also a few special factions for the sandbox and these usually just have the word sandbox appended e.g. EpirusSandbox
