Update: I found the original piece that was lost ! Very lucky....
I need the plastic trim piece that covers the metal bar on the side of the soft top installation. It's referred to as Guide Arm Cover Right and has a part number stamped on the back: 986.561.446.03
The piece on the driver side has a P/N 986.561.445.02 and I've attached a picture of the drriver side piece and picture of where the missiong one goes.