You might want to check out the website RKRvideo
. It is down right now, but they have some impressive cases over there. Getting them to sell you just the case (without a system in it) may be difficult, but it's worth a shot.
Ahh, I just saw on avscience.com that they use an Antec rack-mount case for their HTPC (search that on google, it'll give you a lot of possible links)
If you fire over to antec-inc.com and check out their rackmount cases, you'll find that they're all black. They're kinda pricey too, but they're not low quality.
Anyways, just a few suggestions...