Wish I could help. Looking for some myself. I take off everything when I polish my 914 & had to use my last spare because a tab broke. They get VERY brittle with age. The seals outlast the tabs! Wish there were some way to repair them, since they're invisible, but I've tried every glue out there - to no avail.
Been watching EBay & hate to buy a complete set, just for the backing plate - but will. Good Luck to both of us, though you need yours more.
Pat