Go to Heresy Miniatures and stock up on other modelling supplies at the same time. I have the set of 12 but you don't need them all, the set of six is fine.
http://www.heresyminiatures.com/images/htt01_1.jpg
There is another type which is like a paint brush with a shaped rubber tip, these can be useful.
http://www.heresyminiatures.com/clayshapers.htm
I also have the type which is a wooden handle with a wire loop at each end, I don't like them nearly as much as the metal ones, but it's what suits you that matters.
Most of these can also be ordered through Amazon.co.
uk.
Hope that helps!