First consider the
linux-lowlatency kernel. It's easily available (just install that package and boot to it) and recieves updates. It's built around the generic kernel with configuration tuned to lower latency. This is a soft-real-time kernel.
Given things are going through abstration layers for virtualisation, it's unlikely that the whole stack will be realtime anyway so personally I'd say soft-rt is fine.
If you want to pursue a true realtime system, you're going to have to build your own kernel. All the PPAs appear to have dried up. It's not hard - it's just slightly painful.
Patches aren't available for every version of the kernel but you'll find them here:
I'd also suggest building from the vanilla source instead of hacking a patch onto the end of the standard Ubuntu kernel. If I were doing this, I'd be following this guide: