I would recommend that you post your need for the hubcaps on the PeachParts.com forum using the Parts Wanted section. This forum is used by thousands of Mercedes owners. It is free.
HAVE HUB CAPS FROM LATER MODEL 123-14 INCH WHEELS. CAN SELL $100 INCLUDING SHIPPING [ WITH CLIPS]
New ones are available, but fairly expensive.
I need the 14 inch rims for 1973 450sl