The Jelly Bean update started rolling out to the Sprint variant of the Galaxy Nexus three short days ago, but if you still haven't gotten it or are rooted and have been waiting to install it manually, you can now grab it directly from Google's servers.
Before flashing this, a couple of things need to be in order:
You must be on the latest Sprint OTA (FG01).
You must be running a custom recovery, have an unlocked bootloader with the stock recovery, or be rooted with a stock/locked device.
Once those requirements are met, you're only a flash away from jumping up to Android 4.1.1.