never seen that piece repro'd, but if anyone has them it'll be a big truck/bus parts house, not the light truck repro vendors, they're an aftermarket thing, not GM .... might be able to fab something yourself
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics