Classic Mercedes enthusiasts often recommend forums like Benzworld.org or forums.mercedesclub.org for used parts or leads. Haynes or Chilton repair manuals might contain part numbers, though finding free PDFs online can be unreliable. Consider local scrapyards or Facebook groups specific to your model. Lastly, don't rule out Authentic Classics entirely; compare their landed cost to other options and factor in return policies before making a final decision. Good luck!