As an IE80 user who has used the supplied case about twice before disgustedly leaving it aside as a trophy, I feel your pain. The pouches are purchasable from the Sennheiser spare parts store (I checked the Australian dealer's website, and it was like $20 for the pouch itself. Not worth it IMO, for a cheap black soft case which says Sennheiser).
I spent some time walked past many electronics stores in local malls, pondering whether I should buy the cheapest Sennheiser earbud (I think it was the MX370 or something) which comes with a tall leather pouch branded 'Sennheiser' - I'd be buying a $29 earphone for just the case. Luckily, I held off, and my 'carrying pouch' was improvised. I used some Levi's sunglasses pouch with a drawstring as a soft-pouch.
The cable on my left earphone split at the connector after I used the soft pouch, though, so after replacing it under warranty, I decided to use a more sturdy carrying method. I now use the Westone Monitor Vault, $20; it's very sturdy and fits them nicely. Overall, I'd recommend a glasses case or a hard case of some sort over a pouch for portable use as well as for the safety of the IE80s, although I must say they're a tough earphone. Good luck!
Edited by StyleElements - 1/29/13 at 9:29am