If you're looking for a Centauri Carbon gearbox, there's a good chance you're dealing with filament slipping, clicking, grinding, or simply not feeding correctly through the extruder. Luckily, the extruder gearbox is replaceable, so you don't necessarily have to replace the entire printhead if the gears are the problem.
You can find a replacement Centauri Carbon gearbox/extruder gear on Amazon here:
Before replacing the gearbox, I'd make sure you've ruled out the easier stuff first. Check for broken filament inside the extruder, make sure the PTFE tube is clear, and check that you don't simply have a clogged nozzle. All of these can cause similar symptoms.
If the filament path and nozzle look good, I'd take a closer look at the extruder gears themselves. Worn or damaged gears can have trouble grabbing the filament, which can cause slipping, grinding, clicking, inconsistent extrusion, or filament that simply won't load.
Replacing the Centauri Carbon gearbox does require taking apart part of the printhead, but it's still a much cheaper fix than replacing a bunch of parts that aren't actually bad. Take a few pictures as you're disassembling everything so you know exactly where the screws and connections go when it's time to put it back together.
If your Centauri Carbon has extrusion problems and you've narrowed the issue down to the gearbox, I'd probably just replace the gear assembly rather than continuing to fight with it. Replacement parts are fairly inexpensive, and you can grab a compatible Centauri Carbon gearbox on Amazon using the link above.