You don't need specific 'Classic' cases.
80gb classic is basically 'exactly' the same size as the previous 30gb 5g ipod
160gb classic is basically 'exactly' same size as previous 60 & 80gb ipods
So simply if you look for a slimline case to match the older 5 & 5.5g ipods, they will fit your new classic.
All my cases for my previous 60 & 80gb ipods work no problem at all with the 160.....