I’ve just finished a Surface Pro 4 and the left antenna was destroyed when removing the shards of the original screen. Its actually fairly straightforward to create a new antenna using copper tape with conducting adhesive. Remove the antennas unit (4 screws) and cover the area where the broken antenna was and tape round to the underside so the pins on the logic board touch the tape. I added 4 layers of tape to the section where the pins touch the antenna and also bent the pins up slightly to be sure they’ll cotact the tape. Wasn’t all that difficult, don’t bother looking for a replacement antenna, this will be much quicker.