Help with identifying part - trunk bed header piece

Not sure why my truck’s trunk doesn’t have this cab side piece but can someone tell me this piece is called and what is the part number for it? I couldn’t find any diagrams labeling the exact part (it is circled in red and is the piece that is above the bed cab header rail) and wanted to order it to fill in truck cap gap.

 

Update: I called Toyota and they think it is part number 65409-04010 Header Board Rail Sub-Assembly (retails for $380+)

 

Yes, that is the correct P/N for that header rail piece.

 

Thanks for the input. It seems like it is cheaper online than buying directly in-store.