Klein used this same system at one time (pre Trek). The bearings can be ordered at your LBS. There should be a 4 digit number on the bearing seal (Klein used # 6003). Bearings have different numbers depending on inside and outside diameters. Also your spindle may not need to be replaced but you can contact Klein (Trek) for parts. You could also try (very carefully) to pry out the bearing seals and clean and repack the bearings. This might get a little more life out of them.