Hello again. After poking around a bit, and confirming my findings with my fellow Mentors, I’ve got some more info for you. The Gunsmith will only sell the weapons, if the character you are on did not complete the associated quest, prior to the quests leaving. If your character did complete the quest(s), then they can access the weapon though Collections. This is why some characters will see the offerings in the Gunsmith inventory, and some will not.