You've probably already scoured eBay but in case not there is at least one glass only but at a scary price
Here
Or a couple complete with mirror assembly that might be worth investigating
Here
Here
The second one looks promising as you can clearly see the thicker glass surround that gives it away as auto dimming. I managed to get lucky when I bought my CLK and got a perfect mirror for £75. Then went on the hunt for the n/s before realising Mercedes cheaped out and didn't fit them.