hmm. Well, I'd go to Acura and get the parts. Also, there are 2 additional nuts that are on the underside of the bumper. Sometimes they are still there in tack, sometimes they come loose and you need to get them replaced (otherwise you will have nothing to screw your holder into). Check to see if yours are there.
I ended up getting the SOS stealth license plate holder and it requires that those nuts be there (I ended up having to get them separately).