Obtaining kernel sources
From MEPIS Documentation Wiki
You can download your kernel-source package with apt-get or KPackage. You have to put the version number behind the words linux-source-?. For example, if you want the 2.6.23 kernel you would write it as "linux-source-2.6.23", without the quotes. Example:
apt-get install linux-source-2.6.23
This command gives you the version of the current kernel:
If you want to get a version of a kernel that is not in the Debian repositories you can get your kernel from here: http://www.kernel.org/ and click on the "F" to get the full source of the specific kernel.