How to pack and ship a Japanese sword:
In this article I will discuss 3 scenarios: a sword in shirasaya or koshirae, a sword with saya (scabbard) but with no tsuka (handle), and a bare blade. Whichever of these you are shipping, it makes sense to apply at least a thin coat of machine (sword) oil or, better yet, a layer of plastic food wrap (Saran Wrap) to the polished portion of the blade. If your package is opened and examined somewhere along the line (Customs say), the examiner is less likely to leave fingerprints behind

Shipping a mounted blade
It is of utmost importance that the pin through the sword's handle, the mekugi, be firmly in place and sturdy. If the mekugi is weak or missing, and if the package is dropped the blade can crash down inside its scabbard and shatter its kissaki (point). If the mekugi is weak, replace it. You can fabricate a temporary replacement from a bamboo chopstick.
A rubber band tightly round the handle will insure that the mekugi doesn't wiggle loose during shipment. Wrap the sword in plenty of padding: bubble wrap or soft foam, being careful to fold the padding over either end and tape securely to prevent the blade from coming loose in the scabbard along the way. Stiff foam lining the inside of the box is another good idea. Your box should be sturdy. Triangular or round tubes are better than rectangular shapes, as nothing will be stacked on top of them in transit. The cardboard tubes that carpet comes rolled around make extra sturdy shipping tubes.
If you are shipping 2 or more mounted swords in one package it is a good idea to dismount the tsuba and wrap them separately. This will prevent the tsuba of one sword from rubbing against the other. If you do remove the tsuba, wrap a rubber band tightly around the sword's nakago (tang) behind the habaki to take up the tsuba's space and keep the blade from sliding too deeply into the saya. Sometimes shirasaya will split along the glue line at the mouth of the saya due to rough handling in transit. To guard against this try the following. Cut a strip of paper about an inch wide and long enough to wrap one and a half times around the saya about 5 or 6 inches below the koi guchi (mouth or top of the saya). Tightly wrap masking tape around the paper. Now invert the saya on a counter top and force the paper/tape down as far as possible. If you have done this right the paper/tape band will be very tight and prevent splitting. At the other end of the trip it can be slid off and no tape residue will be left behind. The same process forced down the tsuka also makes sense.

Shipping a blade with saya only
Do not ship this combination with the blade in the saya. Without the tsuka and mekugi through its hole there is nothing to keep the blade from bottoming out inside the saya and shattering the kissaki. Tightly wrap the bare blade firstly in saran srap as above, and then in quite a few layers of paper, making sure to fold over both ends and tape the whole bundle securely. Wrap the saya in a few layers of paper and tape this bundle securely. Now lay the blade bundle on the saya bundle, with the point of the blade an inch or so above the bottom of the saya, and very securely tape the 2 bundles together. If the package is dropped it will be the bottom of the saya that will bump into packaging, not the sword's kissaki.

Shipping a bare blade
You will need a piece of very stout cardboard or something similar, or lightweight wood, that fits snugly inside the tube and stretches the tube's full length. Tightly wrap the blade in paper as described in the paragraph above. Securely tape the blade bundle to the cardboard sheet, making sure the tip of the kissaki is an inch or so above the bottom of the sheet. For added protection, you can tie a piece of insulated electric wire through the hole in the tang and cardboard sheet and around the sheet. The cardboard sheet will suspend the blade inside the package and if properly taped won't allow the blade to bump into the package.

Which shipping service to use
Some private shipping services don't insure antiques. If your sword is damaged or lost in transit you may not be covered even if they sold you insurance when you shipped; best to check up front.
I live in the US and I always ship swords with the post office (USPS). They will insure antiques, including Samurai swords, up to insurance limits. In order to collect if there is a loss, however, you have to be able to prove the value, usually with a receipt of purchase or sale. If you can't prove value insurance is worthless. Note: there are private insurance companies that might insure the sword in transit.
USPS registered post is the best option in the US; insurance is available but isn't usually necessary as these packages almost never get lost or damaged.
You will have to cover all places your tube could be opened without cutting into the tube with gummed paper tape. This tape will be rubber stamped when you hand the tube over at the post office, making any attempt to open the package visible. Every postal employee who handles the package between you and the recipient has to sign for it; The post office will know who had the package if there was a problem. If the package spends a night in a post office it has to be in a safe.
As my guy at the post office told me, if you lose registered you lose your job. Registered is less expensive than other services with insurance once you get above minimal value, another advantage.
For international, among the best options is EMS, sometimes called Priority Mail Express International or other names depending on the country. This can be tracked and insured, and imho is very reliable. Please check with your post office to verify the cost, and applicable destinations, as well as length limiations.

Customs
If you are shipping out of the country, you need to fill out a customs form and there are a couple things you need to take into account. There is already a detailed discussion of the customs issue on NMB; you will find it pasted at the top of the For Sale or Trade forum or here's the link: http://www.militaria.co.za/nmb/topic/1860-importingexporting-and-customs-queries-and-advice/ Customs will be on the lookout for ivory. If your shirasaya has ivory eyelets at the mekugi-ana and they find them you could be in trouble. If possible, carefully pry them loose and ship separately. Recently some of us have had customs problems with same', the ray skin under the wrapping of the sword's tsuka. No idea what the work around is for this one; good luck.