I just buy bulk conduit and most important, really soft, fine weaved (if that's the term, where each strand has even finner sub strands) Stainless Steel cable inner cable. galvanized steel sucks and breaks from my experience.
My shop sells me also the little screw type ferrules for both throttle tube and carb bell crank as well as threaded adjusters etc.
Tips?
If your plan this right, the pull cable should never be used as the throttle stop at WOT, the throttle tube should have its own stopper.
Use a dremel cutting disc to cut inner and outer
What are you planning to race BTW?