Porkchop's been my go-to place for 80's style brake cables casings for many years now, as I could never find them anywhere else. Even the older bike shops in my area (American Cyclery, A Bike Odyssey) that still sell C&V stuff, don't sell it anymore.
Especially for the nice clear plastic covered ones.
I'm afraid once those are not made anymore and Porkchop quits selling them, we'll have a hard time finding good equivalents.
Long live Porkchop!!