UPDATE:
Microsoft has made a lot of progress and has now gotten on board with how libraries are normally deployed. You can get it from NPM, Bower, CDN, or create a custom build. Details at http://try.buildwinjs.com/#get
Original answer:
If you install Visual Studio 2013 (you'll need a x86 or x64 PC, not your Surface RT) it will be there. The stuff on GitHub is really not ready for use yet. They promised to publish the files on a CDN when it is. But for now, there are still a ton of bugs that limit it's usefulness outside Windows/WP apps (as you can also see on GitHub) so publishing a compiled build would be counterproductive.
That said... if you look at http://try.buildwinjs.com, you can steal the compiled build it uses :)
- http://try.buildwinjs.com/lib/winjs/js/base.min.js?v1.0.84
- http://try.buildwinjs.com/lib/winjs/js/ui.min.js?v1.0.84
- http://try.buildwinjs.com/lib/winjs/js/en-us/base.strings.js?v1.0.84
- http://try.buildwinjs.com/lib/winjs/js/en-us/ui.strings.js?v1.0.84
- http://try.buildwinjs.com/lib/winjs/css/ui-dark.css?v1.0.84
- http://try.buildwinjs.com/lib/winjs/css/ui-light.css?v1.0.84