It'll take tapered or full 1.5 steerer forks, so look out for bargain 1.5 steerer forks.
As for parts to fitting a tapered fork, it depends on what headset (setup) is current fitted to run the std 1.1/8 pikes(?). It may have a reducers (spacer that fit in) as part of the headset, if so removing the reducer on the bottom cup maybe all you need to do. Otherwise you'll probably need a new headset, bear in mind you need once that fits a 1.5 headstock, not a xx44 (1.5) headstock - if asking anyone tell them its a cannondale 1.5 headstock you need it for.
TBH I've not had to mess with mine much, but my brain melts everytime I get to that question, there are 'help guides' online from the likes of canecreek that should help you pick the right headset but they just make my brains ache.. that might just be me though