I NEED this kernel source installed so I can build a module for an 8812au wifi dongle!
Well a quick search revealed this post which I guess is applicable to your topic
Well AFAIK the buildsystem includes the headers. And this seems to have been the answer to anyone asking for the kernel headers so far.
Found it. sudo apt-get install rbp2-headers-4.9.29-9-osmc
Reinstalled from scratch and installed using June image build, which works “right out of the box”. Spent all night on this nonsense. There is apparently an issue with the latest update and 8812au driver. Back to a fully functional OSMC though.
8812au driver hasn’t changed in some time. The dongle should work without any compiling.