Make friends with the local Benz parts hoarder, eg mb classic star or whatever. A lot of the bigger wreckers have closed down so Facebook marketplace/gumtree isn't what it used to be. There are good deals on some parts via ebay from Turkey (the guy with nos door seals and iirc he does electrical parts too is a good seller) and there's a guy in Egypt too from memory.
Mercedes Classic Centre in Germany can be OK to deal with or tedious, tends to be a bit dicey and definitely pricey (I've only had quotes from them), by comparison amg classic are legends (though I've only had information requests from them). I have second hand anecdotes that the classic centre (in person, sadly) can track down an astonishing selection of parts. German dealerships used to hoard stuff too if you sprichst Deutsch.
The Lithuanian euro parts conglomerates on eBay I find to typically bait and switch or intentionally mislead with a lot if their listings. Huge gamble. I've gotten genuine bmw rain sensors for hundreds less than the dealer but also a random bolt instead of wheel centre caps, so months and dollars wasted.
Stay away from classicparts-nrw, I actually have been there in person and it's a terrible chop shop. Which I forgot and then wound up with a useless pair of shocks with stripped shaft threads
