Sorry, totally forgot to respond to your PM. I'll have to dig them out to get numbers but you are correct on the cover part. You really don't need to worry about the part number so much, just getting the button faces you need. Basically all I did was jump on eBay and used the following searches to find what I needed.

Slk switch (this will pull up window switches as well as others)
You can narrow it down by selecting specific categories or searching more specific but I found looking through the many pages turned up more options.
Here are a couple examples I just found, (just examples, prob not the cheapest ones) a lot of times you can get the whole bezel cheaper than individual buttons.

Window switches

Heated seats etc

The trunk was the hardest. You can usually find a few but from older models so the button is really flat and angled, it doesnt have the roundish divot like the newer ones. May take some time to track the right one down. I searched Mercedes switch or Mercedes trunk switch. The one I ended up getting was from a clk so clk trunk switch will work but usually it returns results with the cluster of windows/mirrors and costs a lot more.

For the climate I searched Mecedes climate, slk climate, clk climate, and a few random variations with heater / AC instead of climate. I can't reccomend the one I got 100% as it will randomly turn on sometimes when in the off position. I don't know if this is a problem with the unit or because of the arm style in the back. On the Chrysler unit there is that big box on the back where the connector plugs in and the plastic arms swivel at the base. The plastic arms on the one I got are just straight plastic so they were more difficult to line up. I assume because they are so tight that the off setting may not be fully in its position leading to the random turning on. I just twist the dial to full and then back off so its not a deal breaker. The SLK ones seem to have the white circles for the most part. Mine was from a CLK and has the black faces. For the best setup I would try to find one that has the same back as the crossfire one but it's not necessary.

I will try to dig up the buttons and give you the numbers for reference but again you're basically just looking for the covers. If you want to do the full conversion using the Mercedes amber lights you will need the guts out of a 2 way switch for the spoiler (the MB trunk and wiper buttons are only one way) I'm not sure about the convertible top. I don't think any of the Mercedes sunroof or convertible top buttons are the same style as the xfire. Painting over an existing button would be very hard to color match. Might just want to paint the whole button and create a custom waterslide decal to put on top and live with no illumination on that one button.