How to install wifi in Macbook Pro
I had the same issue and finally found a fix!!

Not only did I NOT have wifi, but I didn't even have an option for "wifi" under network preferences.  When clicking the (+) under network preferences I only got options for Firewire, Ethernet, Bluetooth DUN, VPN PPPoE, and 6 to 4. 

I tried a number of "fixes" including terminal commands to manually turn the airport power off and on again, deleting the existing wifi option (the one that wouldn't turn On) using the (-) button, and restarting my mac numerous times both in Mac OS and my bootcamp Windows OS. 

Finally, i fixed this issue doing the following:


Restart your Mac. 
upon start-up, hold down the Opt key until you see your drives. 
click on the recovery drive (note: this will not affect or delete any files you currently have). 
login if needed. 
in the top right hand corner you will see the Wi-Fi icon (hopefully). Click the icon and then click "turn wifi Off" and then again click "turn wifi ON" 
restart your Mac again and start it up normally. 
recover from your near-heart attack


Please let me know if this worked.