It's been awhile since I've looked at the Rekluse website, but the Radius CX is everything - clutch hub, pressure plate, steels & frictions, clutch cover, and their expansion "disc."
So to get that it would have to be for your specific model.
The one that you would probably have the best success with is the Radius X, which is just the expansion disc and steels & frictions.
Again, you would have to find a model that is on their website that uses the same steels and friction plates. Without the part numbers being the same, you would have to find someone that has clutch plates from one of the models on Rekluse's site that could measure them for you. Sometimes the difference between the plates are just the thickness. So there may be other models that have the same "tooth" count and diameter that could physically fit in the basket.
For instance, the plates in my 1990 ZR550 and my 2003 KX250 were the same diameter and shape, but different thicknesses. So I could have put the Core 2 out of my KX250 into my ZR550, just would have had to figure out which plates I would need to have the correct overall gap for the Rekluse to work.
The other thing to consider is that the Rekluse expansion disc takes up a bit of room, usually about three or four plates worth. Don't know how many friction and steel discs you have in a CB125R, but there is a possibility that you may not have enough room for it.
I'm having trouble finding a parts fiche for the CB125R, but if it uses the same clutch that the CRF125 does, then I can say that they have a much different basket, hub, discs, and pressure plate design than the CRF150R.