This product is either discontinued or we cannot get that from suppliers.
Qnap KIT-SLIMODDINST-01, Slim Optical Drive Installation Kit, Drive Bay Adapter, Drive Interface mini-SATA, Form Factor Internal, Compatible Drive Bay Width 5.25".
The Slim Optical Drive Installation Kit from QNAP lets you install two slim optical drives in one 5.25" drive bay. Included is a mini SATA cable so the drives can be connected to the internal connectors of your compatible NAS.