Hi, nope, there is no “official” working demo or any “non-official” that I am aware of. To be honest, I am not very familiar with the “spec” and having in mind it’s still a draft:
http://www.w3.org/TR/html-imports/
and the scarce browser support:
http://caniuse.com/#feat=imports
I’d say it’s actually quite unsafe to use it for anything other than testing purposes.
Anyway, here is a good tutorial that might help (I guess you might have already seen it but still):
http://www.html5rocks.com/en/tutorials/webcomponents/imports/
I may try to test this when I have some time but, unfortunately, right now I am not able to help you out with exact instructions.