lemme look it up... he did say that only wizards and witches who were really... important (for lack of a better word) had portraits in more than one place...
okay...
OotP, St. Mungo's Hospital for Magical Maladies and Injuries wrote:
"Everard and Dilys were two of Hogwarts's most celebrated Heads," Dumbledore said, now sweeping around Harry, Ron and Professor McGonagall and approaching the magnificent sleeping burd on his perch beside the door. "Their renown is such that both have portraits hanging in other important Wizarding institutions. As they are free to move between their own portraits they can tell us what may be happening elsewhere..."
So, the most renowned people had portraits in more than one institution (like Hogwarts and St. Mungos, or Hogwarts and the Ministry of Magic). Other people
do have the ability to move among their portraits to different locations, but not that many people, I don't think, would have more than one portrait. Phineas did because he was head of Hogwarts, and he had one at home. But I don't think it likely at all that Sirius had more than one, or even that likely that Sirius even has one that's survived. If he had one at Grimmauld Place, I think his mother would have gotton rid of it. If he had one just about anywhere else, after he was proclaimed a terrible criminal wizard, I don't think people would have been too keen on keeping his portrait around.