What sled? if it's for the one in your name(600sx) and its a twin your only option is a set of twins. Doesn't appear that there was much interest in an aftermarket single for that sled.
You can find a few cans for the stock pipe, or some companies still make or have twins in stock, but they are asking about $500 for a set new. There have been used ones for sale on here and ebay.