How to get missing in-tree kernel module?

Solution 1:

The modules that are not enabled in .config are not built and are not "available".

There is a ton of in-tree modules that are not enabled in Ubuntu .config. The whole point of having a .config is not to compile each and every kernel module. Each distro maintainers choose which modules to include.

You need to build a custom kernel to get this module, or build it separately.

If you want to have a custom module that will survive kernel upgrades, you can make a DKMS package using the kernel source code. But some extra actions should be done to get it built if if is not enabled in .config.