I've been told by SPS that Partners can be added to Outage Notification E-mails by sending an e-mail to
virtualsupport@sage.com - with your name, e-mail and Business Partner ID (Sage Acct #).
Additionally, it's probably worth also navigating to the latest Alert (https://support.sagepayments.com/link/portal/20000/20000/Article/706/Sage-Gateway-Access-Alert), and clicking Subscribe in the paragraph near the top. Allegedly, Subscribers will receive an e-mail any time a future alert is issued (or when an update to the current issue is posted).
For Customers who'd like additional users to receive these Alerts, SPS recommended they do the above Subscribe thing, but it might be worth also sending an e-mail to
virtualsupport@sage.com.