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://repo1.ash.innoscale.net/centos/7.7.1908/isos/x86_64/
http://www.gtlib.gatech.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirror.centos.iad1.serverforge.org/7.7.1908/isos/x86_64/
http://mirror.atlantic.net/centos/7.7.1908/isos/x86_64/
http://mirror.ilumno.com/centos/7.7.1908/isos/x86_64/
http://mirror.arizona.edu/centos/7.7.1908/isos/x86_64/
http://repos.mia.quadranet.com/centos/7.7.1908/isos/x86_64/
http://mirror.us.oneandone.net/linux/distributions/centos/7.7.1908/isos/x86_64/
http://mirror.us-midwest-1.nexcess.net/CentOS/7.7.1908/isos/x86_64/
http://repos-tx.psychz.net/centos/7.7.1908/isos/x86_64/
http://mirror.nodesdirect.com/centos/7.7.1908/isos/x86_64/
http://mirror.net.cen.ct.gov/centos/7.7.1908/isos/x86_64/
http://mirror.hostduplex.com/centos/7.7.1908/isos/x86_64/
http://ftp.ussg.iu.edu/linux/centos/7.7.1908/isos/x86_64/
http://mirrors.cmich.edu/centos/7.7.1908/isos/x86_64/
http://centos.s.uw.edu/centos/7.7.1908/isos/x86_64/
http://mirror.mia11.us.leaseweb.net/centos/7.7.1908/isos/x86_64/
http://mirror.ancl.hawaii.edu/linux/centos/7.7.1908/isos/x86_64/
http://mirrors.rcs.alaska.edu/centos/7.7.1908/isos/x86_64/
http://repos-va.psychz.net/centos/7.7.1908/isos/x86_64/
http://mirrors.ocf.berkeley.edu/centos/7.7.1908/isos/x86_64/
http://repo.miserver.it.umich.edu/centos/7.7.1908/isos/x86_64/
http://mirror.pit.teraswitch.com/centos/7.7.1908/isos/x86_64/
http://repo1.dal.innoscale.net/centos/7.7.1908/isos/x86_64/
http://ftp.usf.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirrors.raystedman.org/centos/7.7.1908/isos/x86_64/
http://mirror.math.princeton.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirror.twinlakes.net/centos/7.7.1908/isos/x86_64/
http://repos.lax.layerhost.com/centos/7.7.1908/isos/x86_64/
http://mirror.grid.uchicago.edu/pub/linux/centos/7.7.1908/isos/x86_64/
+ others, see the full list of mirrors: https://www.centos.org/download/mirrors/
Mirrors verified Mon Apr 27 06:28:48 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://repo1.ash.innoscale.net/centos/7.7.1908/isos/x86_64/
http://www.gtlib.gatech.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirror.centos.iad1.serverforge.org/7.7.1908/isos/x86_64/
http://mirror.atlantic.net/centos/7.7.1908/isos/x86_64/
http://mirror.ilumno.com/centos/7.7.1908/isos/x86_64/
http://mirror.arizona.edu/centos/7.7.1908/isos/x86_64/
http://repos.mia.quadranet.com/centos/7.7.1908/isos/x86_64/
http://mirror.us.oneandone.net/linux/distributions/centos/7.7.1908/isos/x86_64/
http://mirror.us-midwest-1.nexcess.net/CentOS/7.7.1908/isos/x86_64/
http://repos-tx.psychz.net/centos/7.7.1908/isos/x86_64/
http://mirror.nodesdirect.com/centos/7.7.1908/isos/x86_64/
http://mirror.net.cen.ct.gov/centos/7.7.1908/isos/x86_64/
http://mirror.hostduplex.com/centos/7.7.1908/isos/x86_64/
http://ftp.ussg.iu.edu/linux/centos/7.7.1908/isos/x86_64/
http://mirrors.cmich.edu/centos/7.7.1908/isos/x86_64/
http://centos.s.uw.edu/centos/7.7.1908/isos/x86_64/
http://mirror.mia11.us.leaseweb.net/centos/7.7.1908/isos/x86_64/
http://mirror.ancl.hawaii.edu/linux/centos/7.7.1908/isos/x86_64/
http://mirrors.rcs.alaska.edu/centos/7.7.1908/isos/x86_64/
http://repos-va.psychz.net/centos/7.7.1908/isos/x86_64/
http://mirrors.ocf.berkeley.edu/centos/7.7.1908/isos/x86_64/
http://repo.miserver.it.umich.edu/centos/7.7.1908/isos/x86_64/
http://mirror.pit.teraswitch.com/centos/7.7.1908/isos/x86_64/
http://repo1.dal.innoscale.net/centos/7.7.1908/isos/x86_64/
http://ftp.usf.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirrors.raystedman.org/centos/7.7.1908/isos/x86_64/
http://mirror.math.princeton.edu/pub/centos/7.7.1908/isos/x86_64/
http://mirror.twinlakes.net/centos/7.7.1908/isos/x86_64/
http://repos.lax.layerhost.com/centos/7.7.1908/isos/x86_64/
http://mirror.grid.uchicago.edu/pub/linux/centos/7.7.1908/isos/x86_64/
+ others, see the full list of mirrors: https://www.centos.org/download/mirrors/
Mirrors verified Mon Apr 27 06:28:48 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