There are only 9 tab slabs found throughout the world, however there are 12 solos total that are discovered throughout the game for use in single player (and in multiplayer as Ironheade). One is found after a secondary missions, and 2 are granted to the player without the use of a slab. Each has a unique purpose, some for use throughout the world (Summon Deuce, Battle Cry), and others can only be used in stage battles (Rally Flag, Bring It On Home). In multiplayer, the other two factions have a different set of solos to use. Here are the 12 solos found throughout the game.
*Found during the main storyline (Cannot be missed).