If you only need the cartons to fill an opened crate for a display, you can buy a dozen K Ration outer cartons. This means you get 12 sets of all three units totalling 36 outer cartons.
It is also possible to get both the outer and inner carton sets for that extra touch. Fill the inner cartons with a block of wood for shape and weight, and you can open that crate and hand out those rations during a show! (Totals 36 outer and 36 inner cartons!)
12 sets of the outer cartons is $25
12 sets of outer and inner cartons is $40
You get 12 outer (and inner) cartons of the Breakfast unit,
12 outer (and inner) cartons of the Dinner unit,
and 12 outer (and inner) cartons of the Supper unit.