I think what your are looking for are called 'bottom bracket guides' or 'bottombracket cable guides'. Extremely common, every LBS should have dozens laying about. They can be found in the QBP (Quality Bicycle Products) 2005 catalog on page 594.
2004 Raleigh Talus, 2001 Motobecane Vent Noir (Custom build for heavy riders)
campagnolo either currently makes or used to make a steel one...I'm currently looking to buy one of those steel ones myself. At the least it looks like the cable shouldn't bind so much when the bik gets all nasty.