Where to get rear shelf for 560?

[OB Joe]

I am planning on putting some rear speakers in my 88 560sl but I do not want to cut up the original rear shelf behind the front seats. Does anyone know where to buy just the rear seat shelf? I can only find it as an entire carpet set for over $500 which I do not need nor do I care to spend that much.
What I anticipate is cutting out speaker holes, placing the speakers in the easily removable shelf and wiring them with quick connectors. That way I can simply remove the whole shelf, speakers and all, and slide back in the original shelf whenever I want without any hassle.
Thanks if you can help, thanks anyway if you cannot.