Scott,
I have been doing this for 30 years. Here's the deal. You can order a key only or a tumbler and key from any dealer staffed with qualified parts personnel by VIN. I would suggest tumbler and key since the key alone will be almost as much. MB has a few corporate rules. You will need to prepay for the special order. You will need to show ID and proof of ownership before they give you tumbler and key. They will not mail both the key and tumbler, because of possible mail theft. I would suggest trying your local dealer again and ask to speak to the parts manager. If the guy you talked to before is the parts manager, you're just going to have to drive to next closest dealer. I have noticed many times in my years that too many sales clerks tend to make up stories rather than admit they don't know the answer to a question.