The brackets are probably on the rig the bumper was harvested from. I'll bet you can call that salvage yard and ask them to pull them off and ship them to you. Another option would be to call Shrockworks and see if they'll sell you a set of brackets only, but that would take longer. They're probably pumping out a few sets now because of the recent group buy, and I'd bet you could get them to make you a pair for not a ton of money (relative to the cost of a new bumper) while they have the jig set up.