inetdvd.com
I have always bought extra Xbox cases from these guys to replace the games that come with the crappy cases that don't have the pop-up center.
If you're looking for the closest Xbox case match, go with the "grinch green". Not 100 percent, but damn close.
They also have TONS of others, including double disc cases, PS2 cases, etc.
Shipping cost is a bit on the high side, but the cases are a real bargain.
They'd easily do an order of 100+, as they are one of the biggest case suppliers on the WWW right now.
Hope that helps!