Many of the old (antique) door knobs were held onto the connecting shaft with a set screw.  Today's doorknobs will not do this properly.  Find an old lock set.  Loosen the set screw to the point a good tug will pull it off but has enough pressure to hold in place.  This will require an older lock set.  Look at second hand store, garage sales, flea markets and antiques stores.  There are also companies that deal in hardware restoration (go into an old condemded building and pull all the useable hardware then resell at high prices).