Can anyone give me the part number for the black plastic underside grill for a 2007 GCSRT8? I dont need the outer colored bar part. Just the underside that is black plastic.

the front bottom one ????

If it's the main grille you are referring to, it comes only as an assembly which includes the backing mesh. Part # depends on color and list is around $300.00.

If it's the lower grille mesh, p/n 05030066AB (MSRP $162.00).