CompUSA currently doesn't have the Nikon SB-600 listed on their website. I called them up and the SB-600 is not listed in their inventory system. On the phone they could not confirm whether the SB-600 is discontinued or they just dropped it from their catalog. Here is a live support chat session that I found online, indicating that the SB-600 is discontinued at CompUSA (see similar story from Staples here):
Please wait while we find an agent to assist you...
You have been connected to J***** J******.
J***** J******: Thank you for contacting us today, how may I assist you?
Me: Hi J*****, I'm looking at the Nikon SB-600 flash right now.
Me: It appears that it is "unavailable"
Me: Do you have any idea on the status of the object?
Me: Is CompUSA just out of stock, or has it been discontinued?
J***** J******: Let me check on that for you. Please give me a minute or two.
Me: Great, thanks.
J***** J******: Thank you for waiting. With regard to your inquiry unfortunately it seems the item has been discontinued. We do not have any information on the future availability of this item on the CompUSA site.
Me: Hmm, okay. Thanks so much for the information, J*****!
J***** J******: Have a great day, and thanks for providing us with the opportunity to assist you today!