I gave you a link to the RCM in my post. Parts are easy to find unless they are body parts, you cant get those other than from a salvage yard. Engine/transmissions/chassis parts are found by searching for "Mercedes 2003 SLK320 <insert part here>".
If your car is an SRT, then "Mercedes 2003 SLK32 <insert part here>".

AS Wad has said, needswings.com (Rob) is a great guy to go to. He is about the ONLY guy you can admit it's for a Crossfire, everywhere else, you better claim it's an SLK320 because "Crossfire parts" don't exist in the computer parts tables of your local parts store (and even a lot of online stores).