I've had bad luck keeping the 626/a (bottom-bracket guide for FD and RD cables) rust-free, but I see them on other bikes without rust. How do they do it? I think I'd have to clean the thing after every ride, What am I missing?
Alternatively, is there a substitute in stainless steel or some other rust-resistant metal?
Thanks in advance.

those are chromed finish... if yours rusts easily, the chrome has been violated, and it was then re-polished..

the only way to prevent re-rusting is to get one that still has it's chrome intact, then keep it fairly clean and mostly dry..
salt from the ocean or road salting can eat chrome.
scratches speed up the process... i cringe when i see scotch-brite marks on once shiny chrome.

or just use PB Blaster and alu. foil to clean the rust... it makes the parts look better, for a while.... sigh.

there are several on Ebayt.. in the 25 to 60 dollar range... some look brand new/NOS... others, not so much.

search: Campagnolo 626/a cable guide
there's a NOS one for $35, plus $4.91 shipping...
being sold By Dicknosebikes, in Denver... if he's got decals for that shop, i'd pay for one.

Thanks for the explanation. Went with NOS Suntour. Not as snazzy as Campy, but more in tune with my bike.