Hi Strat.
I can't be absolutely certain about the SC3, but I have an SC4, which I assume is a very similar design, only larger.
The jaw carriers on the SC4 are not easy to remove, there is a locking circlip ring inside the chuck, which prevents the jaws being wound fully out. The Sorby Patriot and Nova2 chucks are the same, and require fully disassembling to remove the carriers.
It is my understanding that removable jaw carriers is one of the significant differences in the design of the Axminster chucks vs the SC4/Patriot/Nova.
So, I think, if removable carriers are a must, Axminster chucks are the place to go. This may be why SC3 carriers are hard to find as they will only be needed to replace damaged parts.
Hope that is helpful (and correct).
Foxy