Gallinger,
The part number is MA688Z/A and it is called "Airport Extreme Wireless Upgrade Kit for Mac Pro"
If they can't find it after you tell them that, then say that it is behind the back counter in the PC section of the store, in a little white box.
If they can't find it after all that then you should give up on them and try asking Carbon Computing (http://www.carbonation.com), they people who work there are really nice and helpful.
Good luck!
The part number is MA688Z/A and it is called "Airport Extreme Wireless Upgrade Kit for Mac Pro"
If they can't find it after you tell them that, then say that it is behind the back counter in the PC section of the store, in a little white box.
If they can't find it after all that then you should give up on them and try asking Carbon Computing (http://www.carbonation.com), they people who work there are really nice and helpful.
Good luck!