My local LBS (Rat Race Cycles) will almost certainly have some, so I can nip round tomorrow and get one. Then have the one being delivered later this week as a spare. If they don't have any, I'll call in at Brixton Cycles instead. Cheers.
Just realised I can't actually pop by Brixton Cycles as the bike I would normally use to get there is currently being worked on (by me). LBS didn't have any stepped ferrules, so gonna have to wait until the one I ordered arrives before finishing off the build.
Now, why don't I have one of those right here?
Got one on order. Until then, I guess I can install the brakes and cable up the front mech.