I believe if you've ever placed an order direct from them, you're placed on it. Otherwise, I'm sure they're happy to place you on the mailing list if you just call one of their London stores.
enquiries@edwardgreen.com
You would need to click on CONTACT in the upper right corner of the website ... almost impossible to find.
P.S.: another email address is sales@edwardgreen.com
Thank you. I don't know why I couldn't find the address before.