So a few specifics - doesn't have to be a Buffalo spindle. It does need to be a6 spline, 5/8" diameter, at least 15" long with a spline length of at lease 6-1/2" and a taper chuck fitting.
Thanks for the clarification Bob - when I saw you responded I was hoping it was to say you had what I needed on the shelf. . Turns out after destroying the chuck I discovered it was a 33B - threaded chuck. Not sure if the spindle came threaded from the factory or a PO got creative and put a 1/2 - 20 thread on the taper.