Can you get a replacement through QMT/PM? Otherwise you can get precision lead screws with an AME thread and turn the ends if you have access to a lathe. There are also on-line vendors that will turn them to your specifications. Ball screws are a bad idea for manual lathe, in particular with climb milling. I have used CNC mills in manual mode and one needs to be very careful that the manual feed doesn't get away from you.
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