We’ve never seen such a note of desperation about a mezzaluna before. Did you break your friend’s mezzaluna in a fit of rage and now you have to replace it before she notices? Was a mezzaluna used in the commission of some nefarious crime, and Scotland Yard is questioning you about the whereabouts of your mezzaluna, which has suddenly gone missing? Or do you just have an immediate, overwhelming need to mince some parsley? Clearly, our imaginations are running wild - not unlike the British tabloids.
The wonderful, two-handled, curved-blade rocking knife you seek is often called a mincing knife, and should be widely available at cutlery shops throughout the UK. Certainly Harrods has them for sale. Scott & Sargeant Cookshop, which has a retail store outside London in Horsham, West Sussex, has a variety of single- and double-bladed mezzalunas, all with chopping boards. Similarly, The Cook’s Kitchen, which is apparently only an online merchant, has a lovely variety of mezzalunas.
In this country, you can buy them at Amazon.com.