what repository is the webmin package located?

[Tomoki Taniguchi]

I was trying to install webmin on my amd64 gutsy server.
but when i try "sudo apt-get install webmin" i get this response

<snip>
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package webmin is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package webmin has no installation candidate
</snip>

i figure it's either not in my repository list or
there is no amd64 webmin pacakge.
in case the amd64 was the problem i tried to install on a i386 gutsy server.
i got the same thing.

my /etc/apt/sources.list contains
<snip>
deb http://jp.archive.ubuntu.com/ubuntu/ gutsy main restricted
universe multiverse
deb-src http://jp.archive.ubuntu.com/ubuntu/ gutsy main restricted
universe multiverse
deb http://security.ubuntu.com/ubuntu gutsy-security main restricted
universe multiverse
deb-src http://security.ubuntu.com/ubuntu gutsy-security main
restricted universe multiverse
deb http://archive.ubuntulinux.jp/ubuntu-ja gutsy/
deb-src http://archive.ubuntulinux.jp/ubuntu-ja gutsy/
deb http://archive.ubuntulinux.jp/ubuntu-ja gutsy-ja/
deb-src http://archive.ubuntulinux.jp/ubuntu-ja gutsy-ja/
deb http://ja.archive.ubuntu.com/ubuntu/ gutsy-updates main restricted
universe multiverse
deb-src http://ja.archive.ubuntu.com/ubuntu/ gutsy-updates main
restricted universe multiverse
deb http://archive.canonical.com/ubuntu gutsy partner
deb-src http://archive.canonical.com/ubuntu gutsy partner
<snip>

TIA,
Tomoki Taniguchi