No, it was never offered as a replacement part - it is installed in the engine case at the factory and is a special bearing - you cannot waltz into a bearing supplier and buy one across the counter. To the best of my knowledge the only company that offered it was Hot Rods in their crankcase bearing kit (which is very hard to find).
Kit # TBK0011 for 99-04 and kit TBK0012 for 05-14
The bearing is so fragile the average mechanic cannot install it with out damaging it. I have only changed one in 40 years of working on motorcycles and it was not because it was worn out, it was either damaged by water or by someone trying to remove it.
If I was restoring a TRX400 for someone and could not find the bearing or a replacement engine case, I would take the case, the old bearing and the shift drum to a machine shop and have them machine a bronze sleeve to take the place of the bearing.
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