Hi Jamie, welcome to Vector Linux.
Your first stop should be the gslapt package manager. It is on the start menu. First, click edit > preferences > sources, then check the lines for "patches" and "testing". Let it update, then use the search field to look for your package.
If that doesn't do it, you may enter a request for the package in the forum. Or you can just search for a compatible Slackware package. For VL 5.9 that would be Slack 12. Sites like www.linuxpackages.net
have a good selection. Download the package, open a root terminal and change to the folder where you downloaded the package to. Enter command "installpkg <nameofpackage>". Note that unlike gslapt, this will not pull in dependencies, you may have to resolve those yourself.