Looks like the original author decided to upload the source code after all: https://github.com/DrBeef/QVR
Now also as DaydreamVR version: https://github.com/DrBeef/QVR-Daydream
Based on QI4A & Darkplaces. Lets you play Quake1 based games with Google Cardboard VR headset.
This is the code for QVR version 1.0.2_3 (May 27th 2016).
I am not affiliated with the original author of the Play Store app (https://play.google.com/store/apps/details?id=com.drbeef.qvr). But the original author did not create a GitHub repository for this code and has chosen to provide the code only to people who purchase the app (the author included the sources in the .apk as necessary by the GPL license).
I am mirroring this code here for developers of Darkplaces Engine ( https://icculus.org/twilight/darkplaces/ ) based games to more easily make a VR version of their games. If you just want to play Quake1 in VR, I strongly suggest you just buy it from the original author as he did all the hard work to get it running on Cardboard nicely.
For an alternative GearVR version see the original author's website ( http://www.quakevr.com/ ) and Github repository ( https://github.com/DrBeef/QuakeGVR )