That's the 2nd generation iPod Nano. I doubt that any retailers still stock them but there is an ebay seller who claims to sell new ones. The 4gb models go for $130-160 + postage. (http://stores.ebay.com.au/e-tech-Unlimited)

Keep in mind that the 3rd gen nanos (wide ones) play video and that their RRP is far less than the 2nd gen.

4gb 2nd Gen = $299.95 RRP
4gb 3rd Gen = $199.95 RRP

I was after a 2nd gen after mine got stolen but couldn't go past the new one - it plays videos and is pretty much the same price brand new from a retailer as the 2nd gen is after being heavily discounted over ebay. Up to you mate good luck.