Someone at Google's mess the links. Here are the correct ones...
NEXUS 5 hammerhead:
https://dl.google.com/dl/android/aosp/hammerhead-kot49h-factory-02006b99.tgz
NEXUS 7 2013 razor:
https://dl.google.com/dl/android/aosp/razor-kot49h-factory-ebb4918e.tgz
NEXUS 7 2013 razorg
https://dl.google.com/dl/android/aosp/razorg-kot49h-factory-49789b24.tgz
NEXUS 4 occam:
https://dl.google.com/dl/android/aosp/occam-kot49h-factory-02e344de.tgz
NEXUS 10 mantaray:
https://dl.google.com/dl/android/aosp/mantaray-kot49h-factory-174ba74f.tgz
NEXUS 7 2012 nakasi:
https://dl.google.com/dl/android/aosp/nakasi-kot49h-factory-5e9db5e1.tgz
NEXUS 7 2012 nakasig:
https://dl.google.com/dl/android/aosp/nakasig-kot49h-factory-83d93b5f.tgz
NEXUS 5 hammerhead:
https://dl.google.com/dl/android/aosp/hammerhead-kot49h-factory-02006b99.tgz
NEXUS 7 2013 razor:
https://dl.google.com/dl/android/aosp/razor-kot49h-factory-ebb4918e.tgz
NEXUS 7 2013 razorg
https://dl.google.com/dl/android/aosp/razorg-kot49h-factory-49789b24.tgz
NEXUS 4 occam:
https://dl.google.com/dl/android/aosp/occam-kot49h-factory-02e344de.tgz
NEXUS 10 mantaray:
https://dl.google.com/dl/android/aosp/mantaray-kot49h-factory-174ba74f.tgz
NEXUS 7 2012 nakasi:
https://dl.google.com/dl/android/aosp/nakasi-kot49h-factory-5e9db5e1.tgz
NEXUS 7 2012 nakasig:
https://dl.google.com/dl/android/aosp/nakasig-kot49h-factory-83d93b5f.tgz