I have made replacement cork stoppers for a 33-key Hooghuys street
organ (LH595).  Champagne corks were used, since there is no damage
from the use of a corkscrew.  I made a jig to fit on my Myford ML7
lathe and used a sanding disc to remove cork whilst rotating the
cork about its axis.

The first sanding leaves the cork very slightly conical; a second
sanding with the cork reversed on its axis results in a slightly
barrel-shaped cork which can be moved safely both in and out of the
resonator.

Ted Bowman