It's a bit of a puzzle, isn't it? This is a little tough to explain with out being there but I will try. You took the nut off, pulled the hub out and the front half of the inner race came out with it, right? If you place the ring of ball bearings back in the outer race where they go and then try to place the inner back where it goes it does not what to fit. If this is your problem, what is happening is as you push the inner into the ring of ball bearings you are forcing them into the outer race. The contour of the outer race is such that it causes the diameter of the ring of ball bearings to close up just enough that you cannot get the inner race into it. What you need to do is to reach in there with your finger and keep that ring of ball bearings pulled forwards toward the inner race you are installing and the whole damn thing will just fall together, much akin to how it fell apart when you accidentally took the hub and race out of it. I don't know if the bearing is available seperately as I have always hung the hub and bearing as a unit. If you have to replace the hub and bearing assembly make sure that you keep pressure on the inner race while you do so. The best way is to grab it up with your hands at 3:00 and 9:00 with your 8 index fingers wrapped around the back and your two thumbs pushing on the race from the front. Keep pressure on it between your thumbs and fingers and then slide it all onto the spindle. If you do not keep pressure on it the front inner race will pop out AGAIN. In fact if you cannot seem to get that inner race back on with it on the spindle it is n option to pull the rest of the hub off, reassembly on the bench and then reinstall as a unit.

Good luck,
Mark