Well so far, no luck, but...

Assuming you have not already...
Go ahead and give your local dealership or two a call to see if Mercedes-Benz has a stock. Obviously, you are not going to buy it from them ($$$$), but it could serve as a good indication of its availability in OEM form.

If they respond with No Longer Available (NLA), then your best bet is probably, used (junkyard) or aftermarket... though, I do not think anyone makes aftermarket dashboards for these cars.

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)