Plastic caps on rocker panel

[Paul Ternes]

I have a 21 Sierra Elevation. I have 5000 miles on the truck and I have lost 2 of the black plastic caps on the bottom of the rocker panels. I live on a gravel road. Maybe that's why they fall off. On a white truck, those 10 caps on each side look terrible. Does anyone why GM put them there and has anyone found a source for them. Getting them from the dealer is like pulling teeth!

[Transient]

I need pictures to wrap my head around this one.  Hopefully somebody else can help out. 

[Paul Ternes]

These are the black plastic caps or plugs in question. The one on the right of the picture is a piece of black tape filling in for a missing cap.