*Spoiler*
We don't really know all of them, but aside from Trade Minister Tagomi and one of his underlings who have confessed to being travelers, we might suspect others: The Man in the High Castle himself. That would explain where he gets films about the past (in a different reality) and the future. It also seems likely that Trudy, Juliana Crain's dead half sister, who appears to be very much alive at the end of episode 2.10 (You have been warned that this might be a spoiler) is a traveler.