I am trying to install packages with BT3 with slapt-get (like the Debian-way). However, it seems I am missing the "sources" file. Ok that we can create, but then any one has actual working sources for Backtrack (or slax) for that matter?

Not sure about Slax but under Debian, you have experimental, testing and unstable. Is it the case the Slax?

I will do some googling on this, but I decided to open a thread for other users and if we end up with a good "sources" file, we can post it here.