You do not need a box to ship them. I have received wheels and tires mounted from Discount thru UPS just the wheel/tire. They put a good sized round piece of cardboard on each side wrapping tape around the whole thing.
I will check with some shipping carriers on Thursday. Thanks.I have done the same as otter mentioned above. Really no need for boxes. Just put cardboard over the wheel faces and than shrink wrap or packing tape