Through some torough testing with our current campaign (about to do the last quest from act 1, currently having 21 fame), I can tell that you are simply unable to get Rune Plate, an Act 1 armor piece from the Labyrinth of Ruin expansion. Other items from that expansion, such as Bow of Bone, were available at the shop.
So that got me wondering, how exactly does fame determine what items you can shop? And how does the seperation of act 1 and act 2 shop cards count toward this? I've seen Tival Crystal (which is an Act 2 item from the base game) come across the shop a couple of times already, even though we are not in Act 2 yet.