The ARVR sample can be downloaded from here:
(see the sample package for Unity under "Digital Eyewear")
The Oculus plugin for Unity can be download from:
(under "Unity 4.x Legacy Integration")
EDIT: note that if you download the latest Oculus Unity plugin v0.8.0.0, the integration instructions are basically the same, except that this line:
must be placed at line number 213 of the OVRCamerarig.cs script.
and these 2 lines:
Vuforia.VuforiaBehaviour.Instance.ApplyCorrectedProjectionMatrix(cam.projectionMatrix, eye == OVREye.Left);
must be placed around line number 444-445 of the same script.