Audi colours have 2 choices:
cheap option which is any audi colour - this would include java green, which Wayside in MK will be getting a R8 in java shortly - i think the car is in hitchen currently.
expensive option is colour to sample effectively which effectively means they can match a colour you send them or specify. If you go to a good paint shop they should have a colour brochure that shows pretty much any colour you could want with an appropriate code for mixing - this would also allow you choice over 'pearl' or 'metalic' etc - I presume this way you could even speciy metal flake if you so wanted...... In theory your picture should be adequate for them to match and send you a sample.
You could if you could be bothered look through something like this:
It gives an indication on colours, you might find a few you like the look of in order to get better samples made up - I had a quick look and it lists a couple of greens for Lambo.
Out of interest as I'm thinking of doing this as well, are you going for bespoke interior as well, or just sticking with the paint job?