[CR]Part needed for GB stem

I have a GB Stelvio RTE stem that is missing the cap or plug that covers the quill bolt. See (the rather poor) pics at:

http://members12.clubphoto.com/bob580816/759223/owner-7c49.phtml

The recess is 13mm across and you can see a circlip in there.

I don't know how vintage this stem is, but it rides atop my mid-'60s Raleigh/Carlton Flyer (if that helps keep it on topic).

Let me know if you can help me out before I resort to carving a cork plug.

Thanks,

Bob Hufford
Springfield, MO