You are looking for Slackware packages that are not provided in the official online repositories of Slackware? Where to get these extra Slackware packages?
The first place to look is the Slackware community in Italy. They are building hundreds of useful and brand-new packages:
Robby Workman is building a lot of current packages like KDE4:
Also Alien provides a lot of good Scripts and Packages:
Another well known place is the LP.net. However the quality level of packages is said to be uncertain in some cases.
If you are willed to build your packages from source take a look at:
The list is not exhaustive and preselected by individual preference. It is intended as a first hint where to start a research. The list is “work in progress” …