Ouch! Sounds like something I'd do.
Depending on how it's bent, I'd suggest laying it flat (grip side up) on a dead flat hard suface like a 1/4" steel plate or better yet an anvil, and tap it with a large rubber mallet or plastic hammer. Look where it "rocks" when on the plate and tap conservatively. Aluminum will expand easily, so be carefully not to bend it out of shape.
I have no idea where to get a single grip.
Pretty dumb, I know... Doh.
I did basically what you describe (only on the corner of a granite countertop) and it's real close, but not quite perfect. Someone who was less OCD than myself would probably not even notice it, but since I do, it's annoying as hell.
I'm going to try to get it as close as I can and live with it, though if it continues to bother me I'll just sell them cheap to a CZer who doesn't mind one of the panels being 99% perfect and pick up some new one's, just sucks 'cause they're kind of pricey and I wouldn't sell these for anymore than $50 without feeling shady about it. Oh well, could stand to loose another ounce for IDPA anyway, if anyone is looking for grips and doesn't mind the left panel only being 99%, PM me...