Headlamp replacement

[snmazer]

Hi all!
While taking the front end of my Hummer apart tonight, I noticed that the headlight lenses are completely covered with "spiderweb"cracks. Very thin, hairline cracks over the entire lense. you can't see it until you look very close to the lense. My H2 is a 2003, and just wondering if I can just replace the lense housing, and not the entire assembly? I assume that the headlamp housing is a standard GM part, assembled into the headlamp assembly? I hope that makes sense!......anyway, does anyone have any info in regard to what I need to purchase, part numbers, etc.
Thank you.
Scott