Saw this on Ebay. Supposedly NOS though close inspection shows a few minor scratches. Hope the link works.
BMW E9 3.0CS CSi 3.0CSL Hella Rear Left Tail light Lens Rücklicht Links NOS | eBay
BMW E9 3.0CS CSi 3.0CSL. Hella Rear Left Tail light Lens. Genuine NOS.
www.ebay.com