Did you follow the instructions?
<
https://github.com/PolymerElements/polymer-starter-kit#install-dependencies>
Particularly :
npm install -g gulp bower && npm install && bower install
It all works fine for me - `gulp` seems to copy bower_components/ and elements/ into dist/ and they're there :
[dist]$ ls
bower_components favicon.ico index.html robots.txt styles
elements images manifest.json scripts sw-import.js
[dist]$ python -m SimpleHTTPServer
Serving HTTP on 0.0.0.0 port 8000 ...
127.0.0.1 - - [24/Dec/2015 11:18:40] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [24/Dec/2015 11:18:40] "GET /styles/main.css HTTP/1.1" 200 -
127.0.0.1 - - [24/Dec/2015 11:18:40] "GET /bower_components/webcomponentsjs/webcomponents-lite.min.js HTTP/1.1" 200 -
127.0.0.1 - - [24/Dec/2015 11:18:40] "GET /elements/elements.html HTTP/1.1" 200 -
127.0.0.1 - - [24/Dec/2015 11:18:40] "GET /scripts/app.js HTTP/1.1" 200 -
127.0.0.1 - - [24/Dec/2015 11:18:41] "GET /images/touch/chrome-touch-icon-192x192.png HTTP/1.1" 200 -
HTH
Max.