It's GM part# 15173619, so for OEM, they're plenty on a Google search
Or call your dealer with your VIN ready. It'll probably be more expensive, but it'd be OEM. But i believe sticker price was $450 for the add on.
Edit: this for $30 seems to be a highly rated backup camera. It's a bit larger, so you'd have to do some fab work (maybe drill a hole below the handle and stick it in). Plus I'm assuming you already have a screen in your truck, otherwise you'll have to get one of the on dash screens.