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Have a look here -may give you some idea
http://www.fullspeedahead.com/product-category/road/?filtering=1&filter_component_type=677
Why would you want to replace it anyway ? What's wrong with it ? If it's worn, a simple change of bearings would suffice ?
I can't think of anything better, unless you are feeling flush and fancy a mix-n-match Hope one. Not to say those are better, just more expensive.
Kinesis 4S Disc has an "integrated FSA type headset"
Anyone know which model it is, specifically, and if there's something else, preferably better, I can replace it with?