In order to conserve the limited bandwidth available, ISO images are not downloadable from mirror.centos.org
The following mirrors should have the ISO images available:
http://mirror.chpc.utah.edu/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.ocf.berkeley.edu/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.keystealth.org/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.genesishosting.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.math.princeton.edu/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.vcu.edu/pub/gnu_linux/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.xtom.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.dal.nexril.net/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.lax.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.atl.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://ftp.osuosl.org/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.esecuredata.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.calgah.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.cedia.org.ec/centos-altarch/7.7.1908/isos/ppc64/
http://linux.darkpenguin.net/distros/CentOS-AltArch/7.7.1908/isos/ppc64/
http://centos.mirror.garr.it/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.hoster.kz/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.ufs.ac.za/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.huaweicloud.com/centos-altarch/7.7.1908/isos/ppc64/
http://altarch.mirrors.theom.nz/centos/7.7.1908/isos/ppc64/
http://mirror.nyherji.is/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.wd6.net/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.gadix.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.xtom.com.hk/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.yer.az/CentOS-AltArch/7.7.1908/isos/ppc64/
http://mirror.nsw.coloau.com.au/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.up.pt/pub/centos-altarch/7.7.1908/isos/ppc64/
http://ftp.rz.uni-frankfurt.de/pub/mirrors/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.uniri.hr/centos-altarch/7.7.1908/isos/ppc64/
+ others, see the full list of mirrors: https://www.centos.org/download/altarch-mirrors/
Mirrors verified Mon Apr 27 06:25:51 2020 UTC
You can also download the ISO images using bittorrent, a peer-to-peer file sharing protocol. The .torrent files can be found from CentOS mirrors. Various bittorrent clients are available, including (in no particular order of preference): utorrent, vuze (Azureus), BitTorrent, Deluge, ctorrent, ktorrent, rtorrent and transmission. Packaged copies of various torrent clients for CentOS can be found in the repositories listed in the following wiki article: https://wiki.centos.org/AdditionalResources/Repositories
The following mirrors should have the ISO images available:
http://mirror.chpc.utah.edu/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.ocf.berkeley.edu/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.keystealth.org/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.genesishosting.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.math.princeton.edu/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.vcu.edu/pub/gnu_linux/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.xtom.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.dal.nexril.net/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.lax.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.atl.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://ftp.osuosl.org/pub/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.genesisadaptive.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.esecuredata.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.calgah.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.cedia.org.ec/centos-altarch/7.7.1908/isos/ppc64/
http://linux.darkpenguin.net/distros/CentOS-AltArch/7.7.1908/isos/ppc64/
http://centos.mirror.garr.it/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.hoster.kz/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.ufs.ac.za/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.huaweicloud.com/centos-altarch/7.7.1908/isos/ppc64/
http://altarch.mirrors.theom.nz/centos/7.7.1908/isos/ppc64/
http://mirror.nyherji.is/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.wd6.net/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.gadix.com/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.xtom.com.hk/centos-altarch/7.7.1908/isos/ppc64/
http://mirror.yer.az/CentOS-AltArch/7.7.1908/isos/ppc64/
http://mirror.nsw.coloau.com.au/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.up.pt/pub/centos-altarch/7.7.1908/isos/ppc64/
http://ftp.rz.uni-frankfurt.de/pub/mirrors/centos-altarch/7.7.1908/isos/ppc64/
http://mirrors.uniri.hr/centos-altarch/7.7.1908/isos/ppc64/
+ others, see the full list of mirrors: https://www.centos.org/download/altarch-mirrors/
Mirrors verified Mon Apr 27 06:25:51 2020 UTC
You can also download the ISO images using bittorrent, a peer-to-peer file sharing protocol. The .torrent files can be found from CentOS mirrors. Various bittorrent clients are available, including (in no particular order of preference): utorrent, vuze (Azureus), BitTorrent, Deluge, ctorrent, ktorrent, rtorrent and transmission. Packaged copies of various torrent clients for CentOS can be found in the repositories listed in the following wiki article: https://wiki.centos.org/AdditionalResources/Repositories