>>>What? It's not cocoa?
Well it is, sort of. It's (heavily)
sweetened cocoa.
Tesco sell their own 'Sprinkles' (99p for 50g). Their website is currently showing 'currently not available' but it might still be worth checking in their stores:
http://www.tesco.com/groceries/Product/Details/?id=274110139
Otherwise, all of the big coffee shop chains (Costa, etc) sell ground coffee, etc, to take home, so it might be worth asking whether they also sell the sprinkles to go with it.