Oh wow, I have heard about this paint before, it's like the world famous tartan paint, but instead of coloured strips, I think your's has rust coloured blotches and sorta white scratchy lines. Oh, and it's called Scratchy Rusty Stuff Green and comes in many shades too.....
If it is original - have a look at the Parts and Paint Sticky at the top of the Defender threads - gives possible colours by year and also some colour swatches
Bets bet might be to take to a paint shop for them to mix to match
When I last looked there were about 70 Landrover greens still listed. I`ve seen your green before on early model 110`s so your best bet would be to try a good paint supplier - Dingocroft have a pretty good website which lists all the LR greens with their colour codes, or send them a better photo (or even better a sample) and they should be able to tell you the colour and what you need. I`d be wary of doing a comparison straight off the screen, your paint is flat and scratched, and the sample colours that paint suppliers show on screen never ever look like the real thing.