Doug, Les Hovencamp at Diamond gunsmithing is the guy to talk to. He worked on my Wifes Flues and did a great job. He said at that time he had some spare parts. Perhaps he can help you out. IMHO he is the guy you would want to work on your Ithaca guns. Here is the link to his web site.

http://www.diamondgunsmithing.com/index.html

Good luck,
Dave B