Microsoft has again uploaded, or made available the files for the Spring Update for Windows 8.1. We have the links for the 6 kb updates intended for x86, x64 and ARM versions inside.
Others have had success doing it differently, but we here at Neowin have confirmed the above to be working. It's also possible that you will already have kb291442 already installed.
You can of course opt to wait it out and let Windows Update work its magic sometime at the beginning of April when it'll be rolled out worldwide. Or take the plunge and install now, please do note that the updates require multiple reboots, and may also be pulled from the download locations at any time, like what happened last time.
If this is the first time you're hearing about the Spring Update (or Update 1) you should probably wait for the official Windows Update roll-out, see what's new here for more details on what the update brings to Windows 8.1.