Your best bet would be to pull from a donor port. You are talking about the small black antenna soldered to the Charge port correct?
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=== Update (12/24/2020) ===
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if you were a business you could purchase it from the following area. But, It will at least give you proper naming to buy on ebay. https://www.mobilesentrix.com/wi-fi-antenna-cable-for-iphone-8-above-loudspeaker