Qwerty sell a reducer kit for cannondale frames. So you could run 1 1/8" if you struggle to find anything you want.
http://qwertycycles.co.uk/products/cannondale-headset-reducer-cdale-to-1-1-8-kp058 or http://qwertycycles.co.uk/products/cannondale-headset-reducer-cdale-to-1-1-8-hd232
These are for 'dales own proprietory headshok headtube, not their current road headtubes.
If you wanted to use a non tapered steerer you can use a step down crown race.
@Howard started
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Qwerty sell a reducer kit for cannondale frames. So you could run 1 1/8" if you struggle to find anything you want.
http://qwertycycles.co.uk/products/cannondale-headset-reducer-cdale-to-1-1-8-kp058
or
http://qwertycycles.co.uk/products/cannondale-headset-reducer-cdale-to-1-1-8-hd232