Kernel headers for downgraded kernel

[Artnal]

Hi there,

Due to a specific issue I've had to downgrade my kernel version for raspberry pi to 4.19.118-v7l. In doing so, I broke my wireguard install, or at least the part of it that relied on the kernel headers. At present, it seems like the kernel is properly downgraded, but the kernel headers are still on their latest version.

I tried
sudo apt-get install raspberrypi-kernel-headers, which results in

Reading package lists... Done
Building dependency tree
Reading state information... Done
raspberrypi-kernel-headers is already the newest version (1.20210303-1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded

sudo apt-get install raspberrypi-kernel-headers-4.19.118-v7l, however, results in

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package raspberrypi-kernel-headers-4.19.118-v7l
E: Couldn't find any package by glob 'raspberrypi-kernel-headers-4.19.118-v7l'
E: Couldn't find any package by regex 'raspberrypi-kernel-headers-4.19.118-v7l'

apt-cache search linux-headers gives a list that does not include the linux headers for 4.19.118-v7l. The only "all" linux-header I get is for kernel v.4.9.0-6. I'm not sure it would be wise to downgrade the kernel that far back just to get the headers...

Would anyone have a suggestion to downgrade the kernel headers to match the kernel version currently installed?
Thanks!

[popcornmix]

https://github.com/RPi-Distro/rpi-source may help

[Artnal]

Thanks for the suggestion. I gave it a shot and ran rpi-source but at the end of the process, the issue remains. I am not sure I am knowledgeable enough in linux to explore further with this tool atm.