What's the name/number for this part? Pontiac Vibe bumper

2003 Pontiac Vibe.  

I am missing the black piece that the bumper cover clips on to at the rear quarter panel.  My usual method would be to find the genuine GM part number and then search for aftermarket version.  In the GM parts diagrams I have looked through it is not listed as bumper components and not listed as quarter panel components???

Long black plastic piece on this left hand side: 

I need the right hand version:

The piece is for this project:

https://grassrootsmotorsports.com/forum/cars-sale/03-pontiac-vibe-awd-auto-w-67k-miles/154433/page1/

I bet the corresponding part for the Toyota Matrix of that year is the same.  Here's a listing for that

https://parts.toyota.com/p/Toyota_2003_Matrix-STANDARD-HATCHBACK-18L-AT/SUPPORT---REAR-BUMPER-SIDE---RIGHT/63176955/5215502080.html

I want to say "Bumper guide", but that's off the top of my head.