There is a package carrier for monolevers, including a vertical member just behind the seat. One of those package carriers/backrest came with my '91 RT when I acquired it. If I remember correctly the package carrier is mounted to the cowl behind the seat proper. I don't recall if a backrest pad is included on the vertical member, but that's not an issue for you. I don't recall if the package carrier is BMW made or aftermarket. I'm thinking BMW. And FWIW, I think that package carrier/backrest is decidedly ugly, being made of flat steel strips bent and welded together.
If the package carrier is BMW made, I would expect it to show up on (REAL OEM?) or another BMW parts vendor on the internet. Somebody here will know the link(s).
Knowing that what I think you want is available, you might consider placing a wanted ad on the IBMWR Classifieds list. Here's the link:
http://marketplace.ibmwr.org/
In the past there have been some would be scammers on the IBMWR list. But they are usually easy to discover by asking questions and asking for pics. A typical response by a scammer that I've received a handful of times read something like
"I have the part you're looking for in excellent condition" This is, of course, a blanket ad response which the scammer copied and pasted in.
I think that the BMWMOA also has classifieds on their website, which you can see if you're a member.
Ken
