If you're talking about the air dam that attaches to the front bumper, you can get it at your dealer for about $35 or here:
http://www.trademotion.com/partlocator/index.cfm?action=getLocator&siteid=55&chapter=ARF3630&appSectionid=2276&groupid=51817&subgroupid=4048&componentid=0&make=25&model=Armada&year=2005&graphicID=3630010&callout=13&catalogid=2
http://www.trademotion.com/partlocator/index.cfm?action=getLocator&siteid=55&chapter=ARF3630&appSectionid=2276&groupid=51817&subgroupid=4048&componentid=0&make=25&model=Armada&year=2005&graphicID=3630010&callout=13&catalogid=2
