https://www.centos.org/forums/viewtopic.php?t=5770
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:
Actual Country -
http://mirrors.pubyun.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.skyshe.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.163.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.zju.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.bit.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.sina.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.lzu.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.btte.net/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.yun-idc.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://centos.ustc.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.sjtu.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.neu.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.neusoft.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.opencas.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.aliyun.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.nwsuaf.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.cqu.edu.cn/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.cug.edu.cn/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
Nearby Countries -
http://ftp.tc.edu.tw/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://centos.cs.nctu.edu.tw/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.yzu.edu.tw/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.ksu.edu.tw/pub/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.stu.edu.tw/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.twaren.net/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.isu.edu.tw/pub/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror01.idc.hinet.net/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.kaist.ac.kr/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://data.nicehosting.co.kr/os/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.navercorp.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://centos.mirror.cdnetworks.com/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.oasis.onnetcorp.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.premi.st/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.neowiz.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.daumkakao.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.readyspace.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://centos.usonyx.net/main/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.vastspace.net/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.vodien.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.0x.sg/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://download.nus.edu.sg/mirror/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.nus.edu.sg/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.yz.yamagata-u.ac.jp/pub/linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.riken.jp/Linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.iij.ad.jp/pub/linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.tsukuba.wide.ad.jp/Linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.jaist.ac.jp/pub/Linux/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.fairway.ne.jp/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://ftp.nara.wide.ad.jp/pub/Linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://www.ftp.ne.jp/Linux/packages/CentOS/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.logol.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.awanti.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.satellite-service.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.vilkam.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.digitalhusky.com/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.h1host.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://centos-mirror.rbc.ru/pub/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.corbina.net/pub/Linux/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.yandex.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.astpage.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirror.tversu.ru/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
Mirrors Verified Fri Apr 22 07:26:31 2016 UTC
Or use bittorrent to download the .torrent files provided.
Bittorrent is a peer to peer download system described at http://bittorrent.com/ and there are many clients available.
These include (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 : http://wiki.centos.org/AdditionalResources/Repositories
