It is generally expected that Google will become rolling-out the Android 5.0 Lollipop update to the past generation Nexus devices from today. However, the company is yet to make any official announcement on this front, Nexus 7 (2012) device owners have received the next greatest thing — the Lollipop factory image.
The download link of the factory image comes directly from Google’s server so it is as real as things can get. The Lollipop make is based on the LRX21P build, which is what the Nexus 9 also performs.
The factory image is just for the WiFi variant of the Nexus 7 (2012), so you’re out of luck if you own the 3G variant of the tablet. You can simply download the factory image from here but you’ll need to know your way around ADB and Fastboot to install it.