I don't think mulberry sells the East-West Baywater anymore. You may be able to get them at the secondary market such as eBay.
Here in the US you can buy M bags via the M website and call the nearest Mulberry store. I suggest the latter, when you buy direct via the website you get charge custom taxes and ver impersonal. Plus it's just nice to call your nearest M store and develop a nice relationship with an SA.
The nearest Mulberry store to me is in San Francisco and my SA is Eugene (I am totally pleased with his customer service).
The East West Bays has been discontinued in the main stores. However, the UK outlets have still got stock in various colours/leather types. I don't know whether the same is true for the US market. You could use this 'outlet' link and ring around the US outlets to check.
PS. It's a great bag - it's my daily workhorse in black NVT, & it's a lot lighter than the full size Bays.