Is it possible to search gerbers for specific parts?
I'm not aware of a way in GC-Prevue to link pick and place files to Gerbers. 

You could get the (x,y) part location from the pick and place file, assuming it's in ASCII format and not something machine readable, and then use that to navigate to the same position in GC-Prevue to find the component.

If whoever is supplying you with the Gerbers doesn't want to share the PCB design files, could you ask them for ODB++ files? It's easier to find components with those.