Need help finding a part number

[Egan]

First off, no joy on http://parts.nalleygmc.com/.

I need the plastic pieces the large clearance lights attach to at the four corners of the roof (SUT). I looked through everything imaginable on that site and couldn't find it. Not in electrical (only shows the lights) and not in body>roof either.

Here's a picture of what I'm talking about. If anyone has the part numbers for each of the four corners, please reply for posterity: