Hi @sirlenerrm
Thank you for your question.
Tickets for September are already available. It can be that the first part of the journey (Milano > Brig, with an EC train) is already fully booked.
You can try and split the puchase: first Milano > Brig and then Brig > Zermatt.
Please call our colleagues at teh SBB Contact Center (0041 848 44 66 88, CHF 0.08/min) to have more information.
I wish you a nice day.
EleonoraS