Buying a partially used seishun 18 kippu

I know I've read about this kind of place before, where you can pick up a partially used seishun 18 kippu for a reduced price.

Can anyone give me an example of where to find one of these stores, i.e. name and adress?

If anyone's done this before is there anything important to keep in mind?

You can look for a "kin-ken shop". They're everywhere.

I assume the name is written in Japanese as 金券ショップ?

Around major stations, not exactly sure where you are but there are a bunch around Shinjuku station.

I will be staying in the vicinity of Shinjuku and yesterday I did go through the process of making a Google Map of all kinken shoppu in Shinjuku-ku.

http://maps.google.se/maps/ms?ie=UTF8&hl=sv&msa=0&msid=...