It might be worth a look at
Car-Part.com.
This a an online database of salvage yards across the country.
I have found several parts, including a set of running boards for my 2003 Avalanche using this site.
If you do not have any luck with a direct search, broaden your search for some more common parts, like a door, hood or tailgate.
Once you find a possible candidate truck and the picture shows the parts you seek, CALL the salvage yard and make inquiries.
They can not list every single part they have available and maybe you will find a compatible truck.
That's how I found the correct running board for my truck.
I found a truck by looking for something else and the picture showed what I needed.
I called the yard, they pulled the running board and shipped it halfway across the country right to my door.