GNU/Linux Ubuntu 20.04 Kernel Source Downloading
Hi! The Tutorial Shows You Step-by-step How to Download linux-image right Version for Ubuntu 20.04 Focal LTS GNU/Linux.
And then linux-image for Ubuntu Focal provide the Headers needed to compile Modules for the Kernel.
How to Download Kernel Source for Ubuntu 20.04 Focal
First see into the Ubuntu Archive.
And then eventually search on pkgs.org.
Finally, try to Search it with Google on Launchpad.