Check out the patch notes for the v18 Kritias Expansion here: http://forums.maplestory2.nexon.net/discussion/45974
Shamisen and and Shakuhachi gone from store
MapleStory 2 Rep: 200
I can't find any mention of these instruments anywhere about why they've been removed and when to expect them back so I'm assuming developers are not aware of them not being currently on the store (?). I know some people have them and theres a news post from September 19 about adding them into the game.