Hate to sound rude etc, but why worry about cupholders? I've made ti a personal rule to not have any drinks in my car, ever.

This was after my sister had coffee in her jetta's cupholder(the same 'slide thing' design you are talking about in the slk320) and she hit a bump and her entire center console was covered in coffee.

Very bad planning to have cupholders in sporty coupes, just my opinion

But to help you out, I know exactly what you are talking about and it seems like you can either use the one from your slk (wouldn't do that because you'd have a gaping hole) or goto a junkyard where an slk320 is wrecked, and take the whole center console and just use what you need to make the cupholder fit into your crossfire. they are designed the same way pretty much so you can take the console parts and mix and match for the most part.