Because of the available source code so called AOSP-based home-made images start to show up. If you want to look for pre-compiled Android 5 images take a look at Twitter and type the following simple search words: Android 5. In case nothing is found take a look at this Google+ -site: https://plus.google.com/+AndersonArag%C3%A3oDev/posts/BkELCnf8MHT with pre-compiled images for Nexus 4 and 5. Keep in mind you do everything at your own risk!
I do admit homebrew images are very tempting - especially at the moment when factory images are not available. Although Google delayed their schedule I'm going to wait until next week and download Android 5 factory images (for my Nexus 4 and 7). They have never let me down and have always worked fine.
My Chromebook welcomes Android 5 Lollipop