This in your /etc/apt/sources.list would get you ymessenger-1.0.4_1
deb http://kambing.vlsm.org/DLL/debian-local stable lokal

At least according to this it would have installed:
root@mrk-fujibox:/etc/apt# apt-cache search ymessenger
ymessenger - Yahoo! Messenger Client
root@mrk-fujibox:/etc/apt# apt-cache policy ymessenger
ymessenger:
Installed: (none)
Candidate: 1.0.4_1
Version Table:
1.0.4_1 0
500 http://kambing.vlsm.org stable/lokal Packages
root@mrk-fujibox:/etc/apt# apt-get -s install ymessenger
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
libssl0.9.6
The following NEW packages will be installed:
libssl0.9.6 ymessenger
0 upgraded, 2 newly installed, 0 to remove and 130 not upgraded.
Inst libssl0.9.6 (0.9.6l-3 Debian:unstable)
Inst ymessenger (1.0.4_1 kambing.vlsm.org)
Conf libssl0.9.6 (0.9.6l-3 Debian:unstable)
Conf ymessenger (1.0.4_1 kambing.vlsm.org)

EDIT: Forgot, you can search for packages/repositories at http://www.apt-get.org/