There were some sets on ebay a bit back although i think they were for alto and tenor - it could be common diameters with alto on most if not all pads, if you get someone with a sop to measure them against an alto to see what you need.
It could be time consuming but try emailing specialist techs to see if they have any laying around, some customers change to conventional pads by choice, even sacrificing a bit of originality and value.