Never mind – I did not read the README.  It looks like it got moved to vault.centos.org.

From: Phong Vo [mailto:pvo@apm.com]
Sent: Friday, March 10, 2017 9:57 AM
To: 'Conversations around CentOS on ARM hardware'
Subject: CentOS 7.2 aarch64 ISO

Hi Jim,

Where is the CenOS 7.2 installation ISO now?  We no longer see it under

http://mirror.centos.org/altarch/7.2.1511/

and http://mirror.centos.org/altarch/7/ has been replaced with CentOS 7.3

-Phong