I don't know what those are called either, but I've robbed them off of scrap bicycles - there seem to be two sizes, the ones on brake cables are bigger and beefier. Looking on Amazon I see this kit for $20 shipped ( HDM Go Kart Racing GX160 GX200 6.5HP Predator 212 196 Clone Carburetor Throttle Linkage Carb Kit ), they call it a "Compression Fitting"
- which makes me want to go look at little brass compression fittings in the plumbing section and see if they'd work.
Sorry I'm not more help
EDIT: go to Amazon, and search for "Cable Adjusters". Lots of styles, I'd definitely look for one made of steel or at least beefy aluminum.