While Devtoolset-3 and 4 are located on the Centos mirror site, yum will not be able to find them as they were not included in the repodata on the site. These were probably excluded because they are EOL (end-of-life), and have dependency bugs (Bug 1410152). Try using the older Devtoolset-3 packages here, which do not have the dependency issues:

https://copr.fedorainfracloud.org/coprs/rhscl/devtoolset-3/

If you really want the packages from the centos.org site, I went with wget to download all the RPMs, then recreated a local yum repo. However, you'll see the dependency issues and yum install devtoolset-3 will fail.

$ wget -r -p -e robots=off --directory-prefix="/mnt/local-devtoolset3-repo" --recursive --no-clobber --no-parent http://mirror.centos.org/centos/6/sclo/x86_64/rh/devtoolset-3/
$ sudo yum install createrepo
$ cd /mnt/local-devtoolset3-repo
$ createrepo --database .
Answer from Kevin on Stack Overflow
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Softwarecollections
softwarecollections.org › en › scls › rhscl › devtoolset-8
Developer Toolset 8 — Software Collections
# 1. Install a package with repository for your system: # On CentOS, install package centos-release-scl available in CentOS repository: $ sudo yum install centos-release-scl # On RHEL, enable RHSCL repository for you system: $ sudo yum-config-manager --enable rhel-server-rhscl-7-rpms # 2. Install the collection: $ sudo yum install devtoolset-8 # 3.
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Centos
cbs.centos.org › koji › buildinfo
devtoolset-10-10.0-0.el7 | Build Info | CentOS Community Build Service
January 21, 2021 - Main Site Links: · Summary · Packages · Builds · Tasks · Build Targets · Users · Hosts · Reports · Search
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Stack Overflow
stackoverflow.com › questions › 53708189 › how-to-install-devtoolset-7-i686-on-centos-6
centos6 - How to install devtoolset-7 i686 on CentOS 6? - Stack Overflow
To install devtoolset-7.x86_64 on CentOS6 is pretty easy: yum install -y centos-release-scl yum install -y devtoolset-7-toolchain However, i686 is not available for download: http://mirror.centos....
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Ahelpme
ahelpme.com › home › linux › centos 7 › how to install new gcc and development tools under centos 7
How to install new gcc and development tools under CentOS 7 | Any IT here? Help Me!
September 5, 2019 - Unfortunately gcc v8 is not available yet in https://www.softwarecollections.org/en/scls/?search=devtoolset&policy=&repo=&order_by=-create_date&per_page=10 ... The GNU GCC 8 has been added in the software collections, you can see here how to install it – https://ahelpme.com/linux/centos7/how-to-install-gnu-gcc-8-on-centos-7/
Find elsewhere
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Linux @ CERN
linux.web.cern.ch › devtoolset
Developer Toolset - Linux @ CERN
wget -O /etc/yum.repos.d/slc6-devtoolset.repo http://linuxsoft.cern.ch/cern/devtoolset/slc6-devtoolset.repo
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Centos
buildlogs.centos.org › c7-devtoolset-6.x86_64 › Packages
Index of /c7-devtoolset-6.x86_64/Packages
This server contains a mix of raw/unsigned packages and/or build logs It should be used mainly for testing purposes
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Centos
buildlogs.centos.org › centos › 7 › sclo › x86_64 › rh › Packages › d
Index of /centos/7/sclo/x86_64/rh/Packages/d
This server contains a mix of raw/unsigned packages and/or build logs It should be used mainly for testing purposes
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Docker Hub
hub.docker.com › r › centos › devtoolset-6-toolchain-centos7
centos/devtoolset-6-toolchain-centos7 - Docker Image
FROM rhscl/devtoolset-6-toolchain-rhel7 USER 0 RUN yum install -y --setopt=tsflags=nodocs boost-devel && yum clean all -y USER 1001 Copy
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Google Groups
groups.google.com › g › vfx-platform-discuss › c › _-_CPw1fD3c
Removal of Devtoolset-6 from CentOS 7.7
As was mentioned on the CentOS ... through vault) to retrieve the packages through yum, or download the toolset packages from the following link: http://mirror.centos.org/centos-7/7.6.1810/sclo/x86_64/rh/devtoolset-6/...
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Ucsd
browndye.ucsd.edu › download.html
Download & Installation
yum install centos-release-scl epel-release yum install devtoolset-9 ocaml expat-devel lapack-devel apbs scl enable devtoolset-9 bash