Recursive directories source

Hi - I use this as a source for helm-for-files while working on small programming projects - for example, currently I include '("/usr/share/gnome-shell/js/" t nil) which allows me to quickly find any of a set of javascript files under this directory structure. These files are installed on my system via an Ubuntu package, so not tracked by git or another vcs; there doesn't seem to be an alternative simple way to cover them as a helm source without modifying the filesystem, though I'd be happy to know if there is one!

Best wishes,
Graham