I've lost my ignition key.

I got a new tumbler from Mercedes which comes with the original key. Can't get the old tumbler out.

I've read alot of howto's and help pages that all begin with:
Insert the old key and turn to the first position. This is no help because I've LOST THE KEY.

Now what?

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)