The two last brigades for the Union VI Corps (Sedgwick´s): Eustis (in front, with Massachussets white flag) and Wheaton´s.
Flag bearers can be easily made from loading figures. Paper flags can easily be printed from the numerous excellent sites available in the Web .
You can also use Confederate figures for Union and vice-versa, in a way that if you have hundreds of stands each can still be unique.
Now only XII Corps is missing for the Union and 2 brigades for the Rebs. But still 31 artillery pieces and limbers(F*****).