/etc/blends/sources.list.experimental is in blends-dev 0.6.92.5ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # If a Blend should be uploaded to experimental it needs a sources.list
# file matching this target.
deb http://ftp.debian.org/debian unstable main
|