Classicparts (not to be confused with Classic Parts USA) still has NOS/OEM grills for 85 -88 C/K. They list for $205 (+ $27 for S&H).
You must be registered for see images attach
https://www.classicparts.com/1985-88-Grill-OEM-GMC-Dark-Gray-w_Single-Headlamps/productinfo/61-265/
For some reason, they warn that these grills are only for use with single headlight systems. I don't know if you have dual beam or single beams. But either way, it shouldn't be an issue. I looked closely at the GM parts catalog and while there is a distinction made for the RPO V22 option (chrome grill), there is no mention of different grills used with SHL/DHL systems. The only thing I can imagine they are referring to is the fact that with the DHL's, the PL/TS assembly mounts to the back side of the middle bar.
Here is an image showing how they sit. There are only two nuts that secure the assemblies to little studs on the bar. It would most likely only require that a couple of pilot holes be drilled into the plastic and then - instead of nuts - the assembly would be secured with screws.
You must be registered for see images attach
I bought an NOS grill a couple of years ago for a restore project (shown below). It is down in my storage garages which are close by. I will check for you if you are interested.
You must be registered for see images attach
BTW - these grills don't come with letters. Hopefully, you still have yours.