How do you get a replacement key for a 1996 Mercedes Benz e320?

The Dealer. With remote about $150, without remote $20, new battery for remote $10 (google it). Most dealers carry the remote housing that your key "blade" portion and electronics can be transfered to. Cost is about $20 to $30. If this about a key with remote that is no longer working check to see if it is properly synced with the car (see you owners manual), very easy to do.