Great idea. The best place is Computer City, at the intersection of 1st Ring Road (???) and Renmin Nanlu (????). There’s an official Apple retailer (not an Apple store, but the next best thing) just outside of the main building on the corner. If you can’t find that though, you can easily find an iPod Touch from other vendors in the same area. They’ll come with a warranty either way. I just bought an iPod Touch for my father there yesterday – it cost 1,900 yuan for an 8gb 4th generation (newest) iPod Touch including a case, screen cover and wall charger.
Also, if you haven’t already, check out our post on studying Chinese with an iPod Touch or iPhone: https://chengduliving.com/studying-chinese-with-an-iphone-or-ipod-touch