Hello all! What is this and where can I get one for my 05 monte?
Thank you in advance

 

That is commonly called a "door sill" or "door sill plate". That specific one I believe was a dealer option. Not sure if it's still available, but PFYC.com also sold them (very expensive in my opinion).
Some people have gone on eBay and bought SS ones (meant for different cars/trucks, but they fit well on the Monte).
I found a vendor years ago on eBay that custom made a pair of these for me (ran me about $80 if I recall).

 

X 2 what The_Maniac said, sometimes if you look in a salvage yard also there might be some there too. Good Luck!