Looks like it's a pretty standard 1 1/8 aheadset.
It may be advisable to get the headtube faced (ensures the headtube ends are 90 degrees to it's axis - or that's the intention) if you're spending ££ on a CK (or for that matter a Hope) - I suspect the bearings might be closer tolerance, making facing more important. Some frames come faced (eg headtube, bottom bracket, disk mounts), but it's often a step which is missed off, presumable to reduce cost, relying on any post-weld distortion of the headtube (etc) being minimal. Certainly for caged ball bearings there's enough slop around that a little misalignment isn't going to notice.
(Some people poo-poo facing but it's certainly a requirement for external bottom bracket bearings, for similar reasons, plus to reduce the chance of stripping the BB threads due to movement from things not being snugged up tight)
FSA make pretty decent headsets for not a lot of money, with some (tho' not all) of them you can drop in replacement cartridge bearings in the event of them getting knackered. Their - plus some of the Cane Creek - headsets (ISTR one makes them for the other anyway) also have a split crown race, which means swapping forks over is very easy.
Hope's a good alternative to CK and are well-sealed (certainly used to be, judging by the one I fitted some years ago).
EBay used to be a good place for CK stuff, but in recent years there's been a general (ie not bicycle-specific) problem with counterfeit bearings on the market, it's possible that some CK headsets available outside the official distribution network could be knock-offs (albeit very convincing knock-offs).
