Available direct off the Scarpa website or from Climb Newcastle, V12 and the Climbing Works. Figured this was the best place to put it. They're using the same last as the other Instincts so I reckon they'll size the same except now you can rip them on and off easier than the laces.
In reply to And Climb: They do look really nice. V12 actually have the lace version for £80, but £110-120 is comparable to the high end La Sportivas. Might grab a pair once my Instinct Laces give up the ghost.
Interesting that the Climb Newcastle website is recommending going up half an EU size from the Instinct slipper.