I would do one of two things.
1. Do what the one guy did in his photos. Before I wrecked my Regal (Don't worry, she is still drivable and running today), I had a sheet metal bumper filler similair to what this guy did.
2. If that is not the route you would like to go, then go to ebay. i can even send you some links if you would like. I have found many Regal / GN parts on there for not too bad of a price. I think the cheapest I saw was all four (Front and rear fillers) for like $250-$275. Hope I was of some help.
Before I can invest in fillers, I need to get a whole new front header panel, bezels, and grille. Then I can worry about fillers. Good luck and happy hunting.
-Terence.