You can get it from here, with this part number 19120589:
http://www.gmpartsdirect.com/
This might help too seabassnfg:
Grand Prixs Of North America • View topic - *** 04+ Grand Prix Appearance Post ***
Personally I prefer the SE Lip too but you could always get the Inferno front with SE Rear, doesn't look too much different and it flows pretty decently.
Any pics of it? I'm curious to how it looks.