I have this coat and it is from Karen Millen, although it is from the spring/summer collection this year, and not available in their current collection. I got it back in May. I know in some outlet villages like Bichester in Oxford and McCarther Glen in Wales they have Karen Millen old stock, i.e. faulty stuff or stuff that didnt get sold from old stock, so it may be worth seeing if they have it.
The product code to help you with your search is CC004 and it does also come in black so please let them know you are searching for the green one.
The price is �250 but if you buy from an outlet it could be cheaper I dont know.
Also its always worth looking on e-Bay as lots of people sell old season stuff on there.
I really love me coat and always get loads of compliments about it, so good luck x