If you don't have a shirasaya, I would recommend thus:
1. Oil the blade. Wrap in ceran-wrap. Cover the tip with a (small) piece of hard Styrofoam. Ensure that the foam is tightly wedged over the entire tip, and that the sword is not poking out the other end.
2. Cover in foam wrap, then in heavy construction paper. Tape.
3. Take a cardboard tube large enough to house the wrapped blade. Cut a piece of plywood in the size of the tube's lid. Super glue the wooden circle inside the lid. This will ensure that the blade will not penetrate the tube, while also ensuring (because plywood is relatively soft) that the blade will not bend it's tip inside the tube either.
4. Place the blade, tip end toward lid, inside the tube. Fill the gaps inside the tube with packing peanuts, if you want to be crazy safe. Cover the tube with the wood-lined lid. Tape.
5. Place inside rectangular box filled with packing peanuts. Ship.