Here's where I bought mine.
http://www.coolerguys.com/
but it's cheaper here.
http://2cooltek.safeshopper.com/1/cat1.htm?83
You will notice that 2 models are offered,the ultra with the Delta fan is noisy,the other is almost as good,but much quieter.
It's also advisable to purchase and use Artic Silver thermal compound.(available at either place).