I'm going to be running a standard 1 1/8" fork in a tapered headtube.

Frame (Specilaized) comes with a tapered headset fitted

"1-1/8 and 1.5" Threadless, Campy style upper with 1.5" lower cartridge bearing"

What do I need to fit my fork?

Thanks

A reducing headset. You'll only need the lower cup (obviously)

http://www.chainreactioncycles.com/Models.aspx?ModelID=18085

Is there an adapter which can be used, rather than changing out the headseat?

I was hoping for some kind of reducer ring

Browsed CRC but can't find anything

E-Thirteen do one. It's on CRC, too.

oooh… got a linky?

E13 do a reducer which works with zero-stack headsets. FSA do one as well, not sure of the details of that one.

if you call up Hope they may well sell you the bottom half of their step-down headset, it's a nice bit of kit.