Certainly a set of the 1930 British Standards exist, for they were studied by Mike Starmer for his British Army camouflage series, and were recently posted on the net by W.S.Marshall. Unfortunately I've lost my connection, but it was on the airwarfareforum board, and at least one other I am quite sure that the other wartime standards exist too, though I haven't seen them myself. From his text, Paul Lucas has.
The point about Azure Blue is that it was in use: it just took the AM nine months to regularize it in an AMO. However, other colours were prepared without ever, it seems, getting into use or even being seen in an AMO.
I believe that Dark Green never changed its shade until the introduction of the Tornado into RAF service. The current Dark Green is certainly lighter and less olive than its predecessor.
There have been a number of sources giving guidance for NIVO. Ray Rimmel, in Scale Models Extra "Scale Colour" gives it as Methuen 27F3. It is usually described as being close to Light Slate Grey 26E3 (or slightly bluer and lighter) but Dark Sea Green 27(E-F)4 and Sea Green 27E(2-3) seem equally close. If your publisher doesn't understand Methuen, an approximate Munsell equivalent is 6G/3.5/0.5. Some recent research has suggested it was lighter than this, and Dark Slate Grey was adopted for FAA use after seeing how effective Nivo was on Heyfords over the sea. Ian Gazely might be able to cast more light on that.
I have found my printing of the 1930 BSC - it says
www.airwarfareforum.com/upld/img/O-1082626102-84GKiri@.jpg. But it doesn't work for me now. The other was Hyperscale, so I'll bet it is still on there.