the one I missed in Dante's first mission was quite out of the way. In the room where you fight the angelos instead of going out the front door, go through that passage Nero went through on the left, keep going and a combat adjudicator should be in the elevator area.
Other than that just try looking up the locations of the secret missions and the combat adjudicators in google or youtube or something, there are some good videos on youtube showing both the locations and guides to the secret missions.
(I hope for the sake of your sanity you have not left out royal blocker and unbreakable like I did)