I've also been looking for a Maxi all over London! It's not personally me checking out the boutiques in London but rather one of my staff who's currently assigned there. I've asked him to order a metallic grey maxi for me but all the Chanel stores he has visited / called told him that they won't have it until late July. I'm waitlisted at the Brompton Road store but I'll be calling the following stores (the bigger ones) regularly just to make sure:
Old Bond Street
Sloane Street
Brompton Road
The numbers of the Chanel stores can be found in the file I've attached.
ray of light, in case you find a Chanel maxi in any of the London boutiques, please do let me know. Thanks in advance!