According to what I found, Jean Christophe Marchand and his friend, Frédéric Simon created this car helped with car designer Pierre Ménard to adjust the design.
Base car, a wrecked DB4 from 1961 was found in Chartres, France, from Jean-Louis Hébert.
Body was commissioned to Shapecraft, Northampton.
Engine was found in England from a dealer that worked on the Zagato's DB4 2VEV, that had that engine before, and shipped to Aston Engineering in Derby to have it fixed. Capacity passed from 3.7cc to 4.2cc.
It was completed in May 2001.
From Aston Engineering's website:
A customer came to us with a sketch and asked if we could build it. The result was this DB4 Zagato, christened the 'Barchetta'.