Ideally they are tapered but its not really necessary. Cork rod in that diameter used to be available and might still be but I haven't seen anything referring to it in a long time. On my horn the recess is not exactly like the Selmer Paris - it has the normal recess but in the center of that is a small bore. The tech had apparently made a pointed cone of cork and glued it into that smaller bore instead of ignoring the bore and just gluing a round of cork into the recess.
Here's something you might find at the home center/hardware store - a little package of tapered cork 'stoppers'. The smallest size can be modified for use at various places on the horn, and short sections of the narrow end can make these little corks, which gives you that taper. The leftover pieces can be used on the G# foot and other similar 'cups', usually with a layer of felt on the bottom for silencing.
Here's something you might find at the home center/hardware store - a little package of tapered cork 'stoppers'. The smallest size can be modified for use at various places on the horn, and short sections of the narrow end can make these little corks, which gives you that taper. The leftover pieces can be used on the G# foot and other similar 'cups', usually with a layer of felt on the bottom for silencing.
