I knew I would want this catalogue some day!  Piano stool parts:

Van Dyke's Restorers, P.O. Box 278, Woonsocket, SD 57685;
order toll-free 1-800-843-3320.  Mine is a 1996 catalogue.

The metal seat adjustment unit part no. S748 is $11.95.  It looks like
a plate that screws on to the top of the stool and comes with the
adjusting screw with attached plate for the seat.  They also list all
the other parts for these stools

John Dewey