AirPort/Bluetooth assembly, minding the fragile antenna Cables

Ouch! Not good.

If you are speaking about the antenna cables they are part of the display lid assembly. You would need to take the lid off completely following this IFIXIT guide: MacBook Pro 13" Unibody Mid 2012 Display Replacement and replace the complete display assembly as Apple doesn't sell the discrete parts within the lid. The other option is locating a junker to steal the parts from. But you may find just replacing the lid assembly will be easier and less risky.

Frankly, if you lost one of the WiFi antennas then why don't you locate a USB dongle and work around the problem. While its not ideal it will get you there.