There are some good 3-disc DVD case covers - these would take up less room then 3 CD cases... or do you mean you want a 3-disc CD case cover?

Here's where you'll find some 3-dsic covers....

Falle's
- the one on this page is designed for a thick spine.

DanB's
- the one on this page is designed for a thin spine.

Rikter's
- again, thin spines.

RixGrafix (username?)
- thick spines.

And finally, more can be found here:
Various Artists
with both thick and thin spines.

And I think my list is even, kind of in chronological order with the newest first and the oldest last... though i didn't deliberately make this order.

BTW: I know Coov has more covers at another location, not just at the "various artists" link - Coov, where can i find your other trilogy DVD covers?