Google has just released the "L" preview factory images for the Nexus 5 and Nexus 7 (2013) Wi-Fi, and you can get them right now. Here are direct links:
- Nexus 5 (GSM/LTE) "hammerhead": hammerhead-lpv79-preview-ac1d8a8e.tgz
- Nexus 7 (Wi-Fi) "razor": razor-lpv79-preview-d0ddf8ce.tgz
Go! And if you're a developer, the "L" preview SDK is available now, as well.