It's name, simply side finger, explains how it is carried alongside the larger katana in a pair of daisho, easily accessable by the warrior on the side of his obi.
You can buy these from the Tenshodo for between 1400 and 1600gil. The guild points for this cap out at 3040, at 300 per. So for about 14-16k, you can get 3k Guild points for Smithing.
a person by the AH sells then about as cheap an the Tenhsindo but i think actully cheaper..i had no windy fame when i went there to do the quest and i bout a kunai for 500 gil 2 wakizashi for like 1,500 and 2 shinbi-gatana's for like 2.3k a peice all..go there if you want good prices