3/4 synchro hub
Inner part that splines onto the mainshaft what you are calling the hub? We replace the entire assemblies in all the transmissions we do so I have buckets full of used syncro assemblies, but usually the outer part is chewed up where it meshes with the engagement teeth. If you need the inner part I'll send you a good used one for basically the cost of shipping.
They are not sold separately because they are match-fit with the sleeve to control the lash& rock of the assembly. You don't simply "throw" them together & get good results. In fact, if you look at them, they are marked so that you can re-assemble them exactly like original.
