Ha! Well my rotor bb is just as good as the day I bought it, but it is on my track bike, not my tarck biek!
As Dammit says, you should be able to remove the bearings from the cup and find a number on them that will correlate with what size you need to order for a replacement bearing.
@roboto Ah yeah didn't think about that, good point, they probably weren't made with us in mind
Unfortunately the price we pay :p