Thanks for the tips. I did search google before posting here 🙂 but was having trouble with finding results because a lot of them were either way outdated (referring to products several years old and long ago discontinued, or talking about compatibility with OS X 10.2 or something) or had misleading information (i.e. product stated PC+MAC but then if you follow the link and look at the specs, it only listed Windows OS under compatible OSes). I was looking to see if anyone here had some firsthand experience.
Newegg link looks promising as it specifically states OS X in the specifications.
Interesting idea on the internal antennas but I am wary as none of them specifically state they work with Macs. I understand where it's just an antenna and electrically it works, but finding room to put the antenna inside can be an issue given the myriad of internal layouts for laptops. Not to mention the issue of possible interference by laying an antenna right next to/on top of other circuitry. Besides, the disassembly of the old Macbook is too involved for this person to do on their own.
It's a piece of copper with a wire and a plug. Your hands, eyes and ears aren'd specifically stated to work with Macs, they do anyways.
Nearly every laptop uses such an antenna. Macs are Intel PCs with special software, that applies to the AirPort cards, too. PCs just call em Atheros-(or Broadcom) based mini PCIe Wireless cards. Identical thing. The antennas are nearly as slim as a piece of paper, they fit under the battery.
If you want to do it right,
remove the display and place them behind it, that's where these things are placed on PCs. Apple places the AirPort antenna there, too. They're located where the coppercolored things are you see on pages 18-20, but attached on the display assembly. Getting a used display and replace it would be even nicer, but it's rather 149$ for a MacBook with defective Logic Board then 1.49$.
Btw, if your Bluetooth works and you don't need that, switch the antenna cables. The antennas work both for WiFi. Quick, cheap and dirty. Only thing that can have happend to your antenna is A) the cable broke or B) the soldering attaching the cable to the antenna broke. Solder in a new cable would probably work, too. Any computer repair shop can do that, but I guess in the US they charge you double when they see the

.