Hi John. The SNCF had quite a few variants of the famous SNCF green. The 306 is a fairly light sienna rich green hue used mainly on passenger cars. The Nord region basically used a deeper variant (Railcolor: vert Est et Nord), which I remember well on the De Caso tank mikados which I ran behind (and even had a cab ride on). On my Nord cars I use that darker shade, the paint manufacturer who caries it in France is AMF 87. Your best bet is AMF 87 railcolor line of paints these are nitrosynthetic paints and they spray very well. Do check though before application if it doesnt disturb the original Aster paint which was celulosic paint (like automobile paints) so that you don't get any blisters.
But EEC regulations are just as drastic here than elsewhere, I remember when I was working in a Paris hobby shop twelve years ago when the EEC almost forced Humbrol out of business, so beware.