I really have no true-based-in-reality idea, but i can speculate.
if there might not be any sword in it then i would suggest making a "frame" out of, well i would suggest a thick poster board, and if need be add some wire for support, it can be on the outside if you are going to cover it. then you could either cover it with pleather( make it and then slide it over, or just cover, fold rough edge, and then hot glue it.) or you could even spray paint it/ paint it and then stipple it. use a paper towel or a stenciling bursh if you have one or just a really beat up brush, like that come with those kidy craola paintset (got to love those things) and dab it so that some of the color comes off (do this lightly) and it will give the simulation of some kind of hide. a toothbrush would work too, come to think of it. if you want the metal look, get some of that silver spray paint that is made to cover metal stuff, and there you go. the intracit stuff can always be added with magic mold and put on right away, or with super glue/hot glue afterwards(watchout, super glue likes to eat magic mold-truns into fun mush!) and then they can be painted without messing up your other paint job.
as said, pure speculation, but that would have to be my suggestion. now i'm just woundering where i got that from...eh.
good luck though.