Rear bumpers without the impact strip have holes for bumper bolts to mount the bumper to the reinforcement.
Rear bumpers with impact srtips have these holes plus holes for mounting the impact strip. There are no rears bumpers that match the totally smooth front non impact strip fronts.
That being said, companies like dynacorn make new front and rears. The rears can be bought either way with impact strip mounting holes or without. The only front they make is the smooth w/o impact strip holes. They have not been discontinued, they never made them in the aftermarket. I've sent inquiries on a few occassions asking if they had plans to make to the front with holes and always get the same answer, "not at this time". I believe it's because they are/were under the assumption that the front pads are NLA. That's true for GM pads, unless you find an NOS set. But, the front pads are being made as aftermarket parts. They aren't the best quality and tend to look puckered when the bolts are tightened., even if let a bit loose trying to avoid the ripple effect.