After I panic posted about needing this part I decided to go to my FLAPS just in case they might have something that would work. Much to my amazement they actually did have a matching part included in an inexpensive generic drum brake kit that covered multiple Mercedes models (but not w124's according to their parts db).

For future reference, in case anyone else is dumb enough to lose this part like me, the kit I bought was at a FLAPS with same name as a well known valley in California. Its details are:

3363 (assuming this is the FLAPS part number)
2005 KIT
DRMHRDWR