Some guys have all the luck (bg).
Do the set screws on the spindle go down into the threaded shaft
or are there tapered spindles that go on to the shaft using
You should be able to find tapered spindles that are threaded to
fit the shaft of your buffer. Using the spindles made for
unthreaded shafts probably would work for a while, but after a
little use the threads would
become worn due to vibration & the spindles would develope more
vibration & be hard to keep tight.
Good luck finding the threaded spindles.