Burst disk leaking on condor tank

I have a leaking burst disk. My fault because I took it out to work on the valve. My disk is actually fine, it is the copper sealing washer that is shot. Where is the best place to get replacement washers? All the copper sealing washers I have are too big. Does anyone know what the original size and thickness of the washer was? I got a quote from airforce but it seems a little spendy. Any help would be appreciated.

-Brian