Like many others my guttering has suffered from the winter weather.
I am pleased to say I have found replacement brackets (RWKFB2WH) with the help of DIY Doctor, even if it was in a roundabout way.
To help any others in a similar predicament can I suggest if you are seeking Marshall Tufflex parts Google "tufflex-drainage.com"
Identify the correct reference number and contact Marshall Tufflex (now Polypipe)on 01709-770000.
If you do not have an account they can direct you to a local supplier.
(get confirmation that this supplier has recently taken stock of your bracket)
In my case I was directed to Betterview Plastics in Rayleigh Deleted - they had a great selection in stock.