I have been in the same situation with you man.
It took me one year by pressing and pressing again and again the dealer for the original parts,asking all the i30 clubs on the internet but with not luck at all.After all, dealer managed to please me,anyway.
You can install the factory armrest as I did!In the picture below you can see what you have to order from your dealer.Actually you need 4 parts,I can give the parts numbers too if you are interested.
View image: 232As for the stereo this is a picture of the back of the original stereo
View image: photo46 zps38ce8a42So I suppose with the correct harness you might have the USB port,probably it may be allready there but not connected to the interface on your panel.I mean that it might be missing only the USB interface ...
Genuine Hyundai i30 2011-2014 Interior AUX iPod USB Port Trim 12V 84760-A6950RY | eBay