For Sale: Slam that stem - low stack headset cover

Right, assuming I get some measurements for my Canyon, I have a few questions - as its 1 1/4" steerer, do you know of a source for the micro-spacers in that dimension?
And would I need a special expander bung to go to the wider diameter of the fork?

You'll need a bigger bore cover for 1.25", I'm not even sure that I have material big enough but I can check; head tube is likely to be >50mm, based on typical 1.125" practice.

You shouldn't need any shims if you take proper measurements and order the right size, unless you have a very low compression ring. As 1.25" is uncommon, the usual suggestion of checking your/your LBS' parts bin probably doesn't apply. I could get shims made, but they would be prohibitively expensive; the ones I had made to go under sprockets were £40 for 10, but it's unlikely that I could get just one or two made for any less as the set up is 90% of the cost, once you've spent half an hour doing the first one of anything, it only adds a few minutes to do each extra one in the same session.

The expander or whatever else you use as the nut in your headset adjuster is obviously different for a fat fork, but that doesn't have any bearing on the headset cover.