We do not keep kernel sources in gslapt.
In a terminal type
This will output your kernel version.
Then go here...http://vectorlinux.osuosl.org/VL64-7.0/kernels/
Then enter the folder that matches up to your kernel version
Download the kernel-src or kernel-stripped-src (kernel-stripped-src should do and is considerably lighter.)
install the file by right clicking on it and selecting install package (as long as your using the Thunar file manager.)
Try to install the nvidia drivers again.
Sounds like your ok with that but try this video.Installing Nvidia Proprietary drivers