Hello Steve,
Are the cables for the brakes/throttle/clutch?
If so, you can get some very small control cables for RC aircraft from any decent hobby shop.
The cable itself can be as small as .032" (0.8mm) diameter with a tube (from memory) about .08" or .1" (2 - 2.5mm), so you should have no problem getting a scale size.
The minimum bending radius for the smallest control cables is about 1.5". The tube is yellow unfortunately but probably wouldn't be too hard to paint black.
I have used this stuff for years and it is very good. I've never used the supplied clevises, I make my own (smaller) fittings and soft-solder direct to the cable.
Check the Sullivan website, their products have been available at every hobby store I have ever visited.
http://www.sullivanproducts.com/GoldnRodMainFrame.htm
Scroll down past the 'Nylon' type to 'Steel Cable Type', note that the cable is steel(stainless) but is plated for easy soft-soldering.
Edit:
Sorry, forgot to mention there is also Du-bro brand pushrods(example picture of 'Micro 30 system' with the clear tube)... same thing, every hobby store I have ever been to stocks this stuff.
http://shop.dubro.com/p/30-micro2-pushrod-system-2-pkg
I can't comment on the Du-Bro gear as I have always used Sullivan, but I wouldn't expect it to be very different. It is a solid rod tho so may not have the bending radius that the Sullivan cable has.
Edit #2:
Also forgot to mention that these cables work equally well in 'push' operation as they do with 'pull'. Model aircraft can put phenominal loads on these cables and I have never had a problem yet.
When the bending radius is pretty tight I usually put a couple of drops of a light silicon or Teflon oil on the cable before pushing it into the tube.