Cloakd Draggon, don't listen to Crawler. He's lying about all those extremely rare portraits. They don't exist. As for the portraits you didn't list or said you didn't have, this is how to get them:
Paige - found in a chest in Bowerstone Industrial sewers near the rebel HQ
Elliot - received randomly as a gift from Elliot while married to him
Elise - received randomly as a gift from Elise while married to her
Ben Finn & Major Swift - received randomly as prizes for getting 2,000+ points in the mortar minigame after the legendary weapon is earned from this minigame
So you can easily get Paige, Ben Finn, and Major Swift in your game, but depending on your gender and certain choices you made throughout the game, you will have to trade via Xbox Live or an offline profile of your own for the Elliot and/or Elise portraits.