I purchased this grille on Ebay for $90, plus $20 shipping.
eBay Motors: BRAND NEW 05-UP CHRYSLER 300 BILLET GRILLE VERTICAL (item 220025869113 end time Sep-08-06 19:47:57 PDT)
The quality is a little flimsy, and comes in 2 pieces - the grille, and the outer chrome molding.
I see this grille show up occasionally on Ebay.
You can try contacting the seller.
You can also get the same one, or similar one for $250 on Ebay, or this site.
2005 06 Chrysler 300/300C Showtrix Billet Grille w/Chrome Shell
eBay Motors: 05 - 06 Chrysler 300c 300 Vertical Billet Grill grille (item 170067019127 end time Jan-10-07 12:26:27 PST)