or o I have to buy new ones? When I bought the car I received one key for the drivers door but nothing for the other doors.

I think you ought to be able to swap out the tumbler from the old one to place in the new one so you can keep using the key.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.