In order to conserve the limited bandwidth available, ISO images are not downloadable from mirror.centos.org

http://repo1.ash.innoscale.net/centos/7.7.1908/isos/x86_64/
http://mirror.cs.vt.edu/pub/CentOS/7.7.1908/isos/x86_64/
http://mirror.vcu.edu/pub/gnu_linux/centos/7.7.1908/isos/x86_64/
http://repos-va.psychz.net/centos/7.7.1908/isos/x86_64/
http://us.mirror.nsec.pt/centos/7.7.1908/isos/x86_64/
http://centos4.zswap.net/7.7.1908/isos/x86_64/
http://mirror.cogentco.com/pub/linux/centos/7.7.1908/isos/x86_64/
http://mirrors.advancedhosters.com/centos/7.7.1908/isos/x86_64/
http://mirror.ash.fastserv.com/centos/7.7.1908/isos/x86_64/
http://mirror.vtti.vt.edu/centos/7.7.1908/isos/x86_64/

http://mirror.math.princeton.edu/pub/centos/7.7.1908/isos/x86_64/
http://repo.miserver.it.umich.edu/centos/7.7.1908/isos/x86_64/
http://mirror.atl.genesisadaptive.com/centos/7.7.1908/isos/x86_64/
http://mirror.ilumno.com/centos/7.7.1908/isos/x86_64/
http://mirror.dal.nexril.net/centos/7.7.1908/isos/x86_64/
http://ewr.edge.kernel.org/centos/7.7.1908/isos/x86_64/
http://mirrors.codec-cluster.org/centos/7.7.1908/isos/x86_64/
http://centos.den.host-engine.com/7.7.1908/isos/x86_64/
http://mirror.steadfastnet.com/centos/7.7.1908/isos/x86_64/
http://mirrors.unifiedlayer.com/centos/7.7.1908/isos/x86_64/
http://centos.sonn.com/7.7.1908/isos/x86_64/
http://centos.s.uw.edu/centos/7.7.1908/isos/x86_64/
http://mirror.cisp.com/CentOS/7.7.1908/isos/x86_64/
http://centos-distro.cavecreek.net/centos/7.7.1908/isos/x86_64/
http://mirror.den01.meanservers.net/centos/7.7.1908/isos/x86_64/
http://mirror.sfo12.us.leaseweb.net/centos/7.7.1908/isos/x86_64/
http://repos.lax.quadranet.com/centos/7.7.1908/isos/x86_64/
http://mirrors.liquidweb.com/CentOS/7.7.1908/isos/x86_64/
http://mirror.dc2.hackingand.coffee/centos/7.7.1908/isos/x86_64/
http://mirror.millry.co/CentOS/7.7.1908/isos/x86_64/
+ others, see the full list of mirrors: https://www.centos.org/download/mirrors/

Mirrors verified Wed Jan 22 13:52:29 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