According to what has been announced by AC Milan, away tickets for Milan v Atalanta (Terzo anello verde-Away Fan with a 4.109 seat capacity), which is scheduled for Sunday 15 May at 18:00 CEST at the Stadio Giuseppe Meazza in Milan, will be available from 10 a.m. on Monday 9 May.

Ticket price: € 9

Tickets can be purchased ONLY AT VIVATICKET points of sale (NOT ONLINE), you do NOT need to be a fidelity cardholder to buy a ticket.
In the pdf below you can find the list of the ticket offices where tickets are sold.