Those shirts unlock by reaching level 3 in the politician career. So the reason you were able to access it before is because someone in his previous household had reached that career level and the shirt was unlocked for that household at which point it will remain unlocked for that household for the remainder of your save. Now that he's in a new household someone in the new household will need to reach level 3 in the politician career, or you will need the mod listed above to unlock it. I think there's also a cheat that unlocks career reward clothing, but I don't know what it is, I use the mod.
