I'm not hopeful, but if anyone has the driver side parking brake backing plate, or a line on one, please let me know.
Mine are rusted af and of course the only one that's (scarcely) available is the passenger side. Without replacement, activating the parking brake is likely to get hung up on the corrosion, or break through it altogether.

Thanks! Here's an image of the part in question:



GM #15111377 REAR BRAKE CALIPER MOUNT

 

Junkyard/Pick-N-Pull/Used Car Parts only part as of now. Sorry to be the bearer of the bad news.
No aftermarket suppler has produced any either. I have looked and I have a buddy who bought a trashed internals rear diff just for the pristine backing plates.

 

Forget Junkyards, they all rusted. Just make one with metal sheets or find similar plate and made the modifications to it.

Send a request to Dorman to make these plates as they do with others plates.
(ACDelco #15111377 and #15111378)