Building Preemptive Kernel for v4.4.38 UbuntuMATE 16

I need to rebuild the kernel for the UbuntuMATE 16 distribution for Raspberry Pi 3 Model B. Are the kernel sources available on a GIT repo somewhere. Is there any chance that a pre-emptive version of the kernel is already present as a verified binary.

Do you have have any recommendations for this procedure that differ from the following: