I ask, as it can be a bit expensive. But theres a few places that sell Apple parts, such as Macpalace.com or AllMac.com (by no means the only sources though; just stay away from welovemacs.com, as they're thieves with an entire thread on them).
You might also want to check eBay or Craig's List for a broken system or case, as it might be cheaper. Assuming the pics are of the actual unit (and you're sure it's the right model you need), and are clear enough to determine any scratches, dents,... With CL, you can inspect it first. Just a thought.