The part number shown in the GM parts guide seems to be incorrect and don't show up anywhere on-line ...
I got some stainless screws in the correct size and had them blackened chemically when I did mine.
One thing I should have done and forgot was to install that whole thing with a really strong double sided tape to hold it down to avoid the wavy look and for it not to rub the bottom of the doors ...
Anyway these are the type of screws I got for mine:
SELF TAPPING POZI FLANGE HEAD SCREW A2