Can I get chrome-devtools to actually search all JS sources?

Yeah, if you want to search within content sources which are scripts used by extensions and the internal browser API, you enable it in the Settings of DevTools and then from any panel in DevTools you can type Ctrl + Shift + F or (on Mac) Options + Command + F (⌥⌘F) to search across all sources, snippets, and files.

Even more helpful to what you may be needing is to set up a Workspace in Settings cog which you can map to a local directory of files which will be available in the Sources file browser sidebar which will also be searchable with the above shortcut.

There is an option under Settings -> Preferences -> Sources called "Search in anonymous and content scripts".

I'm not sure how/when I disabled this but enabling it and restarting chrome has fixed all of my problems.