The Magnum on the left was built by www.performancewestgroup.com and they used many items from www.RKsport.com but I don't see the grill listed as something they sell. You can contact them to get more info.
The Magnum on the right is the concept car, so your SOL on that grill.
IF you are interested in the "honeycomb" style grille like the SRT's have then you can try PM'ing NC-SXT over at LX Forums. I believe he makes them himself and the price is about $150 with shipping. Here is a pic of mine: