The part you're looking for is the Replacement Swivel Ear for Roadmaster Sterling or Nighthawk Tow Bar - Qty. 1 Item # RM-910661.
If you haven't yet picked out base plates for your 2018 Ford F-150 Raptor to go with your Roadmaster Nighthawk All Terrain, Non-Binding Tow Bar w/ LED Lights - RV Mount - 8K # RM-676 I recommend the Roadmaster Direct-Connect Base Plate Kit - Removable Arms Item # RM-524431-5. view full answer...
I cannot find anything on the Extang cover you have, unfortunately. It sounds like the cover you have is an OEM part for the Ford Raptor.
Without truly knowing what cover it is it's going to be pretty difficult to find the correct replacement. The closest thing I could find that matches the pictures you sent in is the Replacement Front Latch Assembly for Extang Revolution Soft Tonneau Cover # EX1093, which will work on the driver's side of the Extang Revolution.
Realistically, we can't... view full answer...