I'd buy one first like HIWYH8R said. The problem is there are two type of cans available. You can go with the GI Jerry can, which is also sold by Blitz. Or the NATO can. There is also a new GI Jerry can that is plastic but I think it's the same size as the original.
BTW: some GI cans are made from aluminum instead of steel. These polish up nicely from what I've seen...