Depending on their size send them Sea Post but you will be limited to size as all cubic dimensions must be no more than 200cm's max thus you will have to do what Luke said and repack around so they can go.
Dont worry if you get knocked back just try another post office. Just make sure they go as 4 separate parcel and make sure you packed em properly..a square rim box will not go.
Also dont send them the same day if they are going to be worth over $1,000 as you may get stung import duties. Customs are not dumb, so sending 4 brand spankers and under quoting them could see you forking out some duties.They are still blitzing on this at the moment. Just send 2 one day and another 2 the next.
Also its worth throwing on insurance..its about 6-800yen extra to insure for 80,000yen.
If you have any questions flick me a pm or if you can wait 2 weeks you can call my ketai. I'm out of Jappa for 2 weeks sorting some stuff out in Korea just pm me for number.
Heres some info from Japan Post site
http://www.post.japanpost.jp/int/use/parcel_en.html