Can't cut the threads with the lathe?
I looked around at some of the usual tool places. It seems that the smaller thread is really strange.. I can't find a tap close enough to work. I did manage to find the larger tap at msc for ~$30. I might try calling roton and seeing what they suggest (they might just sell a tap). I called them earlier today about some of their freewheeling ballscrews and they were exceptionally helpful. Also, they do sell mounting flanges that screw onto the threaded end of the ball nut. I'm sure these would be easier to deal with. I'm not sure how much $ they cost though.