You could just use apt to get the source,
check that the file /etc/apt/sources.list contains a line starting with
deb-src 
and then use the command:
apt-get update
#if you want to download the source into the current directory use:
apt-get source linux-image-$(uname -r)
#if you want the source to be installed in the system directory use:
apt-get install linux-imagesource-$(uname -r)
 
It will download the source in the folder:
/usr/src or /usr/sources