You can get those 3rd gen iPod nano clones with 30-pin iPod connector on eBay, just search "MP4 3rd gen" or something and hunt through the search results. For example I found this interesting page on eBay, 4GB for $48.95 "Buy It Now" price:
http://cgi.ebay.com/3rd-Gen-4GB-MP3-...QQcmdZViewItem
There are no firmware available to make the 3rd gen iPod nano clone have an interface that exactly or closely looks like the actual 3rd gen iPod nano.
YZ Digital and that other place that was mentioned only sell in wholesale, so meaning that you have to buy a certain amount from them (usually a lot).
I would suggest you also look at iOffer, I found a nice offer from them that's worth the look:
http://www.ioffer.com/i/iPod-Nano-St...-Slot-37573906
The 3rd gen iPod nano clones can fit the 3rd gen iPod nano accessories.