hello Jonny m,
Welcome!
The chance to find a NF gas tank is very small, especially for the CF, considering the number of moto produced for this model;
A bigger chance for the Militare;
I suggest you to repair the tank ,using on of the products available on the market;
I Just repaired the tank of one of my Guzzi, using the Tankerite;
my tank had a big hole on the top and a multitude of pinholes over the entire surface;
I Obtained a very good result